An Applesana forum poster has found references to a MacBookPro6_1 and MacBookPro6_2. Current MacBook Pros are 5,5.
9 to 5 Mac has also heard that Apple Store Geniuses are being trained on new quad-core MacBook Pros with delivery of the machines expected at the same time the newly announced quad-core iMacs ship in November.
Since Apple uses notebook components in the iMac, they usually keep the MacBook Pro at parity with the iMac. Therefore, it is likely that if the MacBook Pro is to receive quad-core processors next month, it will be Core i5 and/or Core i7 processors.
I do find it a little odd that Apple would justify changing the version of the MacBook Pro from 5,5 to 6,1. A version change like that would usually mean something a little more significant than the addition of quad-core processors.
Update 10/27/09: Gizmodo has heard from Apple that “the holiday lineup is set.” Originally Gizmodo had said that there wasn’t going to be any new Apple products this year, but was later corrected by Apple with the new quote. It’s hard to tell what the change actually means but I think it’s safe to say there won’t be any new products announced and available from Apple this year.