AppleInsider says "speed bump" in November.
Penryns are getting speedbumped 133 MHz in Q1 2009. Also, a new 2.0 GHz $348 quad-core (Q9000) coming then too.
Mobile Nehalem is not coming until late 2009 (quad-core) and January 2010 (dual-core).
In regards to November 2008 vs. Q1 2009, remember that the last iMac update was in April 2008, 3 months before the 1067 MHz FSB (Montevina) Penryns' launch. The iMac's Penryns (at least the 3.07 GHz one) were 10 W hotter at the same clock speed as the Montevina ones. So November makes sense, and we could see 3.2 GHz as the top CPU in those iMacs (with 2.53/2.8/2.93 GHz for the others).