Apple tends to refresh all products annually... the iPhone is the biggest exception to their "standard" refresh practice... according to history, it was "due" in June, but it has yet to be officially announced.
That said, they tend to refresh the MacBook Pro in February-March each year.
As with most technology, the innovation is coming pretty quickly, so waiting is always better in terms of "bang for the buck". But that does little to help you if you need a new device. My most recent non-MBP laptop was a 17" HP. When I moved to the MacBook Pro, I went with the 15" model. I recently purchased a new 2011 version (handed the old one down to a family member). My only regret was not opting for the hi-res screen. The 1440 x 900 is good enough, but I wish I had opted for the 1680 x 1050. However, those models are hard to find in the stores, and come packaged with other beefed up specs that I didn't specifically want (at prices that I didn't want to pay)... You can get the hi-res screen without the other "bumps", but only via special order from Apple, so I went with the standard 1440 x 900 resolution.
The 13" MBP with it's 1280 x 800 resolution just seems too small for everyday use, IMHO.
And the quad core i7 processor is the only way to go...
Here's a good resource for what and when to buy, based on Apple's "expected" device refresh schedule:
Mac Buyer's Guide: Know When to Buy Your Mac, iPod or iPhone