I believe it was talked about at SDCC '08 about ending the Ultimate comics. I believe Ultimate Fantastic Four will be wrapping up but that really was the only thing mentioned. Though there's still Ultimatun limited series to start (I believe in September/October?) and word has it they'll be another Ultimates series to come from that. So there's still quite a bit of new stuff to look forward to from the Ultimates universe.
I only really (really) enjoyed Ultimates 1 and 2. I hear 3 is crap so I haven't bothered. The only title from the Ultimate universe I'm following is Ultimate Origins.