So, I'm finally at least *thinking* about frameworks and their usefulness, or lack thereof, for $foo.

I've got an inherited site that apparently was written by a Prototype lover(?), well, at any rate, it *uses* Prototype, Scriptaculous and a tad bit of YUI, near as I can tell (several hands have been in the pot) and I've been looking at JQuery in order to add autocomplete support to a fairly decent local search engine.

My JS foo is pretty limited, mostly because I learned PHP first and have done most of the heavy lifting on the server side. I think I understand *why* to use a framework ... (who has time to reinvent wheels when you can buy a car just down the street) ... but what are the pros/cons of each, how difficult is it to switch a live site from one to the other, and which should it be?

I apologize if this is tantamount to flamewar fodder --- that's not my intent. I just need to get up to speed, and would appreciate your thoughts and pointers to favorite resources that might help me decide on the direction I should take.