Is it worth it to use AdWords to drive traffic to a content site with AdSense ads(I'm not talking about an MFA site)? Do people who have come to your site through your AdWords ad come back?
If your site has somthing worth coming back for, and if your adwords ad is relevent to your site, i'm sure some would come back.. probably..
If you have unique content, advertising it will bring recurring visitors and even links. And if you bid low, but still get your ads shown, you can probably still make money off the adsense ads in the short run. That's called 'arbitrage'.
Worth it depends on what you're aiming for. When I started my forum, I used AdWords to drive traffic to it. When people posted, I made sure they got answers to their questions. To me, it was worth it to get my forum off the ground, although the AdSense did not cover the cost of the AdWords. As my forum grew, eventually the AdSense covered the cost of AdWords. Now I make more each month than AdWords costs, but not enough to cover the expense of the server (although there were two months where it did last year). If I were on shared hosting it would pay for it. So initially it was worth it to me to help establish my forums. It is still worth it to me to drive traffic to my site. My niche is very competitive, and I am able to choose keywords that people search for so they can find my forums even for words and phrases that are not part of my content. For instance, my site is optimized for the keyphrase "baby forums" and "baby talk." It is impossible to optimize for all phrases, such as "baby bulletin board," "baby discussions," "baby chat," "baby help," "baby advice," etc. Then there are all those permutations to do with pregnancy, pregnant, adoption, ttc, trying to conceive, etc. With AdWords, I can drive traffic with all of those phrases and any others I can think of. It helps me to get the right people to my forums, and in turn a lot of them become part of the community. What do you want to get out of AdWords?