There are very many "Is mining worth it?" threads on this board - I suggest you start by reading through them rather than starting yet another one. I hope I don't come off as being mean, because I don't intend to be, but this topic has just been beaten to death IMO. And, really, nobody knows for sure - it all depends on where the price of Bitcoin goes (and how fast the difficulty increases).
Sorry to plague the site with a duplicate thread. I was just trying to post something in the noob section to get my account rolling. This was the first to come to mind.
I'm pretty sure, what with my free electricity, it could be profitable to start mining, but I'd have to do it EXTREMELY efficiently. i.e. used or wholesale prices, and lots more of this CPU mining that I have right now to accelerate my payoff.
Speaking of difficulty, what determines it?