This issue reminds of a question I've wanted to ask you for a while. It seems like more and more we are running across different SEs experimenting with different rankings for different situations (different IPs, different browsers, different customizations, etc.)
Do you see this as a fad or a direction with a future?
Depends on the engine and their amount of resources available. It all goes back to who has the people in place to do the research on the features. With millions of views a day to analyze, they can make some sound judgments of where to put their best efforts. The only question is if they have the right people to look at the data they already have on hand.
I think it is pretty clear that customized delivery is not only a good thing from a site owners point of view, the larget corporate sites have to do it just to keep up.
I do quite a bit of custom delivery for one medium concern that has outlets in Europe. We deliver up to 20 variations on a page and in cerrtain circumstances a localized custom page. If a guy my size finds it benificial to do it for a client, I can only imagine the reward that an SE could find by doing it.