FindWhat is probably the third largest PPC advertising traffic source and delivers fair amount of traffic for most keywords. For the same number of keywords, the amount of traffic you will get will be slightly lower than that of Overture/AdWords.
And I have seen that the conversion rate is not as good as Overture/AdWords. However, FindWhat is a lot cheaper than Overture for almost all the keywords and hence generally, my ROI from FindWhat is as good as my ROI from Overture.
Another advantage of FindWhat is that your listings can be exported to Lycos Insite AdBuyer (insite.lycos.com).
I findwhat.com to be pretty good. I deal with mostly smalled engines just because I have clients that don't want to break the bank... Perhaps you might try Ah-Ha.com as well... they have seemed to distribute their bids to well over 1000 smaller search engines.