A while ago we had a big debate/argument about whether it makes sense to
return partial HTML snippets from "ajax" (or really, um, "ajah", in this
or something in between; or maybe it depends on the app, heh.
Anyway, I ran accross (on reddit I think) this interseting blog post by
the developers of the ruby "Basecamp" app, explaining how they use
where the UI really requires it; and in particular how they then have to
pay a lot of attention to server-side caching to get the very snappy
performance they want.
Some may find it interesting.