Matt Cutts posted a video in response to a user question regarding Google and their methods of penalizing sites. Matt goes on to explain that there are two classifications of penalties to include “Manual” and “Algorithmic” penalties. Manual can include spam reports while algorithm based penalties could include keyword stuffing, cloaking, etc.
-If you are effected by a manual penalty, you can submit a reconsideration request and if Google feels you have a case, they will immediately include your site to back into their index.
-If you are only effected by an algorithm based penalty, you will continue to be penalized until you modify your site to comply with Google’s standards.
I have embedded Matt’s video below for viewing:
What @MattCutts didn’t express was the amount of time the algorithm passes back over the bad site after flagging.