I thought I would provide my opinion on this whole situation...
From rumors that we have seen, the MBA seems to be updating, yet keeping the C2D processor. If Apple did update to the i3 processor, then the MBP and MB would need to be updated too. Reason for this is that a MBA would take all attention away from MB or MBP 13". It doesn't seem Apple would make this change. Unless, they update the MBP 13" and MBA, then keep the MB as product which utilises the C2D processor.
Additionally, if Apple did upgrade the MBP it would only bump up speeds in the 15" and 17" models. The 13" model would POSSIBLY, but unlikely be upgraded to a core iX processor. It is really quite impossible to tell. Some are saying Apple will wait for Sandy Bridge. SB isn't going to be released just yet, and even if they release in Jan 2011 (which is very early so it seems) then Apple wouldn't upgrade their processors until Feb 2011 or after. Note how long we waited for Arrandale processors. This wait until Feb 2011 would be 10 months since their last release, which is quite long, and if you're looking for an update now, it might not be the best decision to wait. Apple could potentially upgrade the processors AND design now, i.e. 10/2010. This means the next update wouldn't be released until maybe WWDC 2011. Also, 10.7 is probably going to be released then, so this could be a perfect time to release a new set of MBPs to be the first laptops running the OS by default.
So, an upgrade now could work quite well from Apple's perspective. However, to me it seems that unless a new design is being released, not much can be done to the MBP 15"/17". Upgrading these two models without a design change might not attract many new customers, probably making this not economical from Apple's point of view. So, I think that unless a design change is going to be released (which is likely, but not desperately needed) then I wouldn't hold off much longer than 20 October.
Just my opinion. At the end of the day I could be 100% wrong
