<p>Pros. and cons? how long do you use it? What about jambi?</p>

I've used Qt on a couple of projects I did in c++ on several platforms over a period of seven years.  I think it works pretty well and definitely was quicker for me to develop a decent GUI app on the Mac than plodding through a language I didn't know (Objective-C) at the time.
I think the signal/slot mechanism is a bit funky but isn't horrible.  Once you're use it for a bit, it's not a show stopper.  The connection stuff is easy to bungle up (or at least it was) and it's always good to check the return on those because your app will go merrily on its way and not tell you that it didn't work.
I've never used jambi.