You can do this but i think sometimes that this can effect the amount of money you get per click.
(This just my own opinion) Have you thought about selling banner advertising spots on certain area's of your websites? I find adsense by far the safest route and they always pay on time.
Andre There is no real answer to this, you need to test it for yourself. Im with Smowtion, Adsense, Adbrite, Bid Vertiser, and a couple others.
It's really all about balance but I have find that the above works best for me personally.Most other PPC - context sensitive or otherwise - programs pay peanuts compared to adsense.