You can get a few microBTC out of free ad-supported sites but if I understand Bitcoin correctly that creates LOTS of inputs for my future transactions which will make it have fees of 500mBTC per kb, rendering the reaping essentially useless.

Am I missing something? Should I just stay away of these sites?

I know the profit is poor even if no transaction fees were involved but it seemed like a great way to make some of my friends "mine" some microBTC.