At the current difficulty of 3,370,182 according to this page:
http://www.bitcoinx.com/profit/

You should manage to mine about 0.0821 BTC per day.

At the current exchange rate of 13.62 USD per BTC
that works out to about $1.12 worth of bitcoin per day.

So the question is, how much extra electricity does your computer use to calculate hashes at full speed 24 hours a day, and how much does that electricity cost?

Clearly if it increases your electricity costs more than $34 per month, you'd be financially better off turning off the computer and using the $34 per month to purchase bitcoins rather than spending $35 per month (or more) to mine $34 worth of bitcoin.