I did this adwords -> adsense and made lots of money in 2005 and 2006 but in May 2007 Google started using landing page factors in calculating the quality score and I couldn't do it anymore. I wasn't aware that it was possible anymore.
I have tested Yahoo -> AdSense. Spent ~$100, made $200+ Quite good ROI Anyway, to play like this you need couple of accounts and earnings spread across them to not flag the account for manual review. GL