Unless you're willing to invest a fair amount in dedicated hardware, plus the running costs, then I wouldn't bother.
As I've said before, it's not a process whereby you earn an amount based on the work you've done, it's a lottery based on who completes the work - the final piece.
You may be lucky, but because the "professional" miners are able to complete many more calculations per second then they are much more likely to get that final piece, and take the prize. They'll probably be working in syndicates, and may each be running several dedicated machines.
Here's a link listing some of the machines dedicated to bitmining:
https://en.bitcoin.it/wiki/Mining_Hardware_Comparison
About a year ago or so I remember a lot of discussion over the cost / benefit of just the electricity, and whether it was really worth it. Of course, with the value ballooning recently that calculation may be less balanced, but with the number of competitors probably joining the hunt then you are still less likely to win, so perhaps not.
Of course, you could give it a go on a crappy old desktop (with half decent graphics card(s) to do the processing) and all you're losing is the cost of the leccy, but don't expect to become a millionaire - you missed that boat by a fair few years now.
EDIT: And take a look at this, gives a profitability calculator:
http://www.bitcoinx.com/profit/