dusky - 8:08 am on May 14, 2010 (gmt 0)
Probably by using yahoo.tld/search?...instead of bing.tld/search?...
The above may read as a cheeky answer, but what I mean by that is, there will be no altering at all in the algo IMO, there will be added ads and their own links and stuff. In addition, I suspect they will use their own crawler in parallel to bing's to feed the bing index as part of the partnership agreement we were not told about, they have more experience and crawl the web better and faster when they want. Two crawlers will be faster in updating the index, each will be assigned certain sections of the web or will run concurrently, one picks up the links, the other double checks and so on, then when all links are collected, they will end up in front of bing's engineers to apply the algo and feed it to the final SERPs index, Y! people won't have access to the bing's algo and architecture, just the raw collection databases to insert in. Can't see them retiring a good and capable crawler.
I am already suspecting that they have started some process, Y! crawler is unusually more active than usual on many of the sites I manage, probably no better time than now when G* is going through the change of life with its mayday update!
teenwolf, you asked for guesses, so I posted one!