I use it for everything, it's well recommended. I'm sure prototype is good now too, but jquery is tiny, and does everything you need, and the code you write with it is tiny too. I have got really into the way you select things to do things to too. As I say I use it for everything at work (though I've not brought all my code on this site up to date with it yet), that as much of a recommendation as I can make. Also there are loads of people writing extensions for it, and it's easy to write extensions yourself.
I am doing a training course in it at work, something I only just found out this week, for the other developers. Before this, I'm going on a course to be taught how to run a training course too, bit odd...
BTW I'm doing my own geocoded feed of pubs and things now, to celebrate this yeah we should meet up for beers soon. Clare is off to Nice with Emma in two weeks, that would be a good time for me, say Friday the 21st? I can't really have any time off so it'll have to be Friday or Saturday, I can come to London or you can come down here.
js: Programming language of the internets, mostly how I make my living.