Having attended library school in a past life, I'm afraid Colette's using libraries as a metaphor for Kiva's inventory didn't quite ring true for me:
I would like to propose that we consider how libraries deal with their inventory decisions. Libraries get new inventory all the time. Interests change over time. Information gets updated. New stories get published. Populations change. Sometimes books get damaged and must be removed from the system. Sometimes the material gets obsolete. Yet the new purchases to maintain the interests of their customers may get to the point of filling the shelves beyond capacity. It isn't feasible or necessarily desirable to keep building bigger libraries to house all the books that are in good enough shape. Part of the book management is to figure out which books are the right ones to keep when shelf space is getting crowded. The time that the book is checked out means that it is earning its shelf space. If a book is only checked out once or twice a year, it can probably be retired. It isn't given premium shelf space to try to generate interest!
1. Kiva is a virtual space. This isn't a matter of not having enough storage space for older items. In fact, the point isn't to store up loans long term just in case someone wants to loan to them -- that's something I think we all would actively like to avoid!
2. Loans represent people, effort, investment. Investment on the part of the lenders, the MFIs, and the entrepreneurs. If a main point of Kiva is to get funding for posted loans (for whomever's benefit you want to argue or believe in), then posted loans not getting funded is an indication of problem(s) in the system.
So I would think of Kiva as a marketplace, not a library. While libraries do also benefit from marketing techniques as Colette described, a loan is not a book that you can check out and return so that it gets recycled to other users!
Maybe you want grass-fed, or chocolate, or calcium-enriched -- or maybe, you just want to buy a gallon of milk twice a week. There's a lot of variety and a lot of opportunity here, but at the current scale of Kiva, some of the milk is getting pushed to the back without a fair shot at being bought. What to do about it?
Having disagreed with Colette's metaphor of choice, I'd like to add that I did think a lot of her specific examples or suggestions were right on target whether we're talking about books or milk:
There are two considerations. One is main page of the Kiva website; the other is the sort which generates the first page of loans. There is a huge jump in loaning activity once something hits the main page. This main page should be carefully considered as it is a major tool to get new people to explore further into the depths of the Kiva website. The main page should generate interest in Kiva, microfinance and the loans. Thus, I would suggest that the main page is to optimize interest in Kiva. By providing at least one loan that speaks to as many people as possible, this will increase interest and follow through in actually delving deeper to sign up and then make loans. This is the first view someone gets of Kiva. Like the front page of the newspaper, the main page should get people to "buy the paper".
Yesterday, at one point all eight loans on the main page were brand spanking new loans in Bolivia. 800 loans on site, and absolutely no variety. Not one loan had even $25 loaned on it. These loans probably were all loaded at one time from the same partner. Meanwhile, a different Bolivian MFI had almost all 20 of the oldest, ready to expire loans.
For books that are EXTREMELY popular--say Harry Potter when it first comes out, libraries don't even display the books. If someone wants that book right away, one must reserve it through a more involved process. It takes a bit of effort, but it prevents being 20th on the wait list! There is no need to place this book in a really visible shelf because it already has the popularity to take it off the shelf.
In some ways, Kiva is a library. Just like some books get checked out without any special placement, some loans will fund without any assist from the main page. These loans may be brand new countries, small loan amounts, or more favored business types. However, some loans, like some books, will see a huge change in interest by placing them in the premium location. In December, libraries move those Christmas and Hanukkah stories and craft books to a very visible display area. This makes it easy for people to find books that are likely to be of interest, and gathers various levels or topics (art, music, history, and stories) in one area. However, in January a new topic such as indoor games and crafts will appear. Regular rotation of this key display area will increase interest. The main page will clearly change much more frequently.
I would like to recommend some changes to the main page loans:
1. Give loans a chance to be Harry Potter and leave the shelf without taking up prime real estate. A minimum of 24 hours, as long as there are older loans, should be allowed for those who are willing to wade through 800-1000 loans. On the 2nd of the month, even some $500 loans without currency risk and a loan term of 12 months or less will still have lots of space for lenders after a 24 hour period.
2. One loan per country (or perhaps per partner) at any point in time if possible. Variety, please! It will encourage a more diverse portfolio for newcomers, which increases the probability that any particular person will find a loan that is intriguing to them.
3. Try to vary loan term, currency risk, countries, loan amount, time until loan expires and loan type, not all of these at every moment. Rather encourage variety over time. This will keep things fresh.
Ideally, the home page should represent the full variety of Kiva and promote Kiva, loans, and lending.

Realistically, we are all suggesting variations in presentation in the hope of getting any better sampling than what we have.
You know, I started by thinking FIFO was the best option for a default sort.
But now I'd also be okay with Random as a default for the short term.
I hope Kiva will take all the ideas presented here as a pool of suggestions, based on a fair consensus that the current Popularity sort is (too) artificial -- and it's become detrimental to getting the maximum number of loans funded AND/OR accurately analyzing the cause(s) for loans not getting funded.
By weighting extrinsic characteristics like "newness" or "videos" as factors for getting into a high-value display area, the current "Popularity" distorts any view/statistics of funding patterns based on the intrinsic characteristics of loans [country, business, description, etc.] AND/OR lender behavior [having as few externally-imposed constraints as possible makes for more accurate measurement or what does happen].
Basically, I've seen loans with "less desirable" characteristics get easily funded in a single day because they weren't washed off the top of Popularity by a flood of other loans, whereas comparable loans sat for weeks with little to no funding merely because it wasn't the right time of the month. I have one current example that I posted in another thread [http://www.kivafriends.org/index.php/topic,4157.msg69073.html#msg69073] ; I'm sure many others have similar stories.
Of course in the long term there should be an ongoing effort to improve presentation by both Kiva and the MFIs, but that can evolve from what they learn from less contaminated user data. Then, Kiva can go back to trying to influence user behavior -- just work with reality next time, not against it.
Lee
(who actually avoids loans with videos, but loans to Men with Cows. See, Kiva does have something for everyone!)
[Edited to add link to my comparative example and to emphasize that Colette's view of Kiva and mine still come to a lot of the same conclusions.]