Well, we never truly know when the MBP will be refreshed.
The last three refresh's have come 10 months apart from one another:
June 2009 -> April 2010 -> February 2011
So if recent history repeats itself we should expect a refresh around December-January. Although I feel that this fall/winter the focus for apple is the iPhone, iPad and iOS...it wouldn't surprise me to see a MBP line refresh closer to February/May 2012. Additionally, there have been rumours that Apple is creating a MBA-like 15" notebook, which too might push a MBP refresh later.
My point is that nobody really knows when apple will refresh their lines, so you have to ask yourself: Can I wait until Apple refreshes? (not knowing officially when they will release). Or can you live with buying now and enjoying the greatness of a MBP until then.
You are lucky, you are buying at a time when a future technology has just been introduced to the MBP line (Thunderbolt). Therefore, even if you buy now you will not be left far behind because you have a technology that isn't really being used now, but will be in the future.
Here is a link to help you decide for this purchase and any future purchases
Mac Buyer's Guide
Hope this helps.
-bentharbour