Really not that tough of a decision...
There is so much back and forth on this issue, and I don't really understand why. Consider the possible scenarios, which break down in to three general categories: major revision sometime soon, small speed bump sort of revision, or no revision at all. We can assume that there will always be some sort of revision, and MacBook Pro hasn't had a "major" update arguably since June so one is likely in the relatively near term. But likely isn't definite, is it?
What if there is a major update announced in January with February availability? If you order your MacBook Pro today you probably have it before the end of this month. If they do in fact announce something really significant in January, you have a decision to make. Keep your new MBP, or wait a few months more, until they work out the bugs on the new one, and throw yours on eBay. Sure you take a hit for a few hundred dollars, but you've also already enjoyed your MBP for a several months. As further insurance, you can cancel pretty much right up until the time you receive it. So if the rumors firm up between now and December 1 that a major update is coming, just cancel your order. No harm, no foul.
Also consider how badly you really need your new machine. If it's mostly a "fun factor" purchasing decision it's easier, and maybe even more fun, to wait. If there's a definitive reason why you NEED to upgrade just do it. Budget permitting, you can always do it again a six moths from now.
I love to have the latest and greatest, for sure. I had been waiting to order a new MBP to replace my 12" G4 PowerBook. When they announced processor and hard drive bumps last week, I finally pulled the trigger. If (when) they announce something totally irresistible in the future I'll decide if i want to sell the one I just ordered, which by that time will still be a very desirable high end machine, and order the newer one. For a total risk factor of about $500, I can have my cake and eat it too. In the mean time, I'll be enjoying my fabulous new MBP while some folks are still debating the issue. I say "go for it".