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 
case?) requests from javascript; or whether instead modern apps should 
all move toward "javascript MVC" models with most logic in the js layer; 
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 
partial HTML returns to js, and avoid "javascript MVC" except in areas 
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.

http://37signals.com/svn/posts/3112-how-basecamp-next-got-to-be-so-damn-fast-without-using-much-client-side-ui