I do not have any first-hand experience with FastClick, but I generally keep the following in mind:
Companies of all sizes need to be profitable. Larger companies and networks have a higher instance of fraud (or at least attempts thereof) and someone needs to pay the lost money. That fraud doesn't come off the company's bottom line; it comes off of yours.
You may want to send your traffic to a smaller ad network, like
http://www.trafficmp.com/ I have had good success with them. Be wary of toolbar installs, etc. You can contact them and tell them which types of ads you don't want running on your campaigns.