I think I would be going nuts right now, had I belabored this point about a late-2011 "silent update" MBPro and not bought mine in early August.
I would have not had all the enjoyment of my MBPro that I've had, and not moved on with other things in my life.
I worried about having the latest and greatest, but then I started thinking that the "silent update" wouldn't be worth much, since it appears only to be a slight speed bump in CPU. A more worthwhile update will be next summer, when the MBPros with the new Intel Ivy Bridge chips come with USB 3.0. Now that's worth waiting for--not a small .xx bump in processor speed.
If Intel had a hot new chip like Ivy Bridge coming out within a couple months, yeah, I'd wait and get the MBPro then. But IF Apple silent updates the MBPro now (which we don't even know IF Apple will do at all, and have no reason to believe they would!), the difference would be minimal (and there will be NO USB 3.0 ports this year) and not worth belaboring about it for months putting my life on hold obsessing about it. That's just plain ridiculous.
Realistically, best case for any late-2011 MBP upgrade will be a CPU speed bump -- something 98% of people will not even notice. That's it. Finito. We have no solid conjecture that Apple will even release a silent update of the MBP this fall, none whatsoever. Energy-draining obsession.
There will be no monumental change that is worth obsessing about until at least the middle of 2012, when MBPros with Ivy Bridge & USB3 ports come out.
Heck, I'd say that Haswell, in 2013, will be far more exciting than Ivy Bridge is gonna be--Haswell will have a 20x reduction in power usage, all day battery and 10 day standby time.
Plus, Haswell will have the kinks knocked out of it that Ivy Bridge WILL come with, as IB is a major architecture change with tri-gate transistors. Haswell is the one to keep an eye on, for sure.
Get the MBPro now if you want it and enjoy it. You are waiting on something that's probably not even gonna be noticeable. Move on with your life, for cryin' out loud!