FYI: According to a forum I was reading, the consensus says that it takes 6 months of quality posts to generate an income of $100 per month using Google's Adsense.
I have heard this as well. Probably the exception to this as far as it happening faster is you are a blogging maniac like Darrin Rowe from problogger.
I only do a very very small amount of blogging as it is not my focus....I'm up to a whopping $.73 after 1 month. LOL