There's a ton of posts debating the pros and cons of mining vs. costs, but if you're mining on anything more than just your GPU sitting in your main machine, you owe it to yourself to determine your 'Break Even' price of BTC vs. your Local Currency.
It's actually pretty simple. First, figure out how much you spend on electricity mining each month. If you can determine out your machine's power draw with a KiloWatt meter or something of the sort, you can get an approximation by seeing how many watts your machine is pulling from the wall and doing the following:
(Watts Drawn from the Wall / 1000) * 24 [Or however many hours per day the machine runs] * 30 [Or however many days there are in that month/billing period] * Kilowatt Hour Cost [Most power companies will list that on your bill or you can call them and get it]
There's your approximate mining cost for that machine per month.
Then just hit up any of the many Mining calculator's
out there. Plug in your hashing rate and tweak around with the BTC price until you find the price that you'd make back the same as your electricity costs are that month, there's your break-even price.
You'll need to recalculate that at every difficulty jump to find your new Break Even price and if you haven't already paid off your hardware costs, you need to factor that in as well.
Regardless, there's no reason to not be an informed miner and determine what price you will be 'profitable' and at what price you're spending more than you're making and then make intelligent decisions on your own about what works for you.