Well, basically, you tell me: this is a half-second exposure with a lens that cost me two hundred bucks (FA 50 1.4) Longer than I usually go, especially cause subject motion gets to be a real factor long before that, but it so happens I was trying to prove a point last night while we were sitting around, so I actually just stopped down.
(This is with a K20d, deliberately freehand, but I was sitting. )
1/2 sec f6.7, ISO 3200
Basically, the in-body SR will let you use nice and long shutter speeds with any lens, but for things like street photo, you've got to remember they're still long shutter speeds. Subject motion really becomes the limiting factor, but one limiting factor is better than more of them.
I'm looking forward to an eventual K-5: there's more high-ISO capability there, which ought to open things up a lot, regarding exposure choices.