Apple usually updates the MBP every six months. However, it did a small, very small, spec bump to the high end model a few weeks ago. In addition, it also gave the 256 GB SSD option.
Now, I originally thought that was just to hold things over, but now I really wonder if it may be September before there is another speed bump jump. There are no chips unless Apple finally goes with the Core 2 Quad. Or, it will have to wait for Core i7... which some think is next year at earliest.
Seems like a long wait for a new MBP. Seems like six months from now everyone will stop buying the MBP to wait for an update. This caused Apple great problems with its desktop sales. Apple finally made a worthless CPU upgrade in the Mac mini and iMac, but nonetheless people started buying in droves!
The bottom line is no matter how we think about it, we could be completely wrong. Apple could decide to go to Core 2 Quad the day Snow Leopard is released. Or, Apple could forgo all speed bump updates until Core i7 is available???
It is really REALLY REALLY a roll of the dice or anyone's guess!