jQuery on iPhone/Android/BlackBerry
I've used jQuery on iPhone. Remember that Mobile Safari is not an officially supported browser for jQuery. But it's close enough to Safari that most things work.
If I recall correctly, mousedown event doesn't happen until the mouseup happens, at which point both fire. My guess is that most things will work, but you need to test everything carefully.
My experience is that changing the DOM is unexpectedly slow. Things that fly on the emulator can drag on the device. (You mentioned you'd be using emulators--do NOT trust performance you get on them.)
jQuery might be overkill. I ended up relying on XUI, which gives you a lot of the jQuery stuff, but is much more lightweight, and also gives you touch events. http://github.com/brianleroux/xui/tree/master
ppk has begun testing mobile browsers. http://www.quirksmode.org/m/w3c_core.html
Came across this today and remember reading your post on here. Thought I would include the link for anyone that's interested in this jQuery project for the iPhone:
Haven't had a chance to try it out yet, but it seems to replicate a lot of the iPhone interface elements within the browser. I think it shows some promise, and uses a lot of the jQuery conventions.
Do not expect jquery to work much at all on Blackberry. The default browser is very limited in terms of JavaScript and page rendering.
Though opera on Blackberry might be a different story...