My Guess
It all comes down to what angle you use to base your guesses. I'm going to use the Apple.com homepage. Clearly, all of Februay and most if not all of March will highlight the iPad, so I don't expect MBP or any other product updates during this time. iPad is the first new product category for Apple in a while, so I predict they'll want to promote iPad for a couple of months on the Apple.com homepage.
When April hits, they'll update the MBPs with the latest and greatest Intel processor, and Mac Pro with a new design (finally) and new processor. They'll call it the "Pro" update and highlight both on the Apple.com homepage.
In May, they'll update the iMac with not much of a change on the high-end but with the 21.5" getting i3 and possibly i5. The MB will also see a slight update. It probably will be a "silent" update with nothing on the Apple.com homepage but a nice update message on the bottom of the screen.
I have no guesses on the MacBook Air or Mac Mini.
June you have iPhone and I suspect we'll finally see an Apple TV update with a new OS at WWDC.