I doubt ah-ha will give Adsense much competition, but found this interesting article today:
"Web site owners can now share revenue with online advertising service provider ah-ha.com, Inc. thanks to a new partnership between ah-ha and search engine developer Rolist(TM). Under the agreement, approved sites can syndicate content from ah-ha.com via BannerBoxes, a new pay-per-click advertising solution that allows Web site owners to display ah-ha paid listings.
intresting... havent gone so far to look at qualifications for publishers, (eg min page views), but it does seem apart from it being keyword driven rather than content-spidering driven, their key spin is to focus on perceived limitations of the Adsnese program by some (eg. being able to allocated own keywords, flexibility, known commission etc). Downsides would probably be lower revenue per click, much less inventory and variety of inventory. Unknowns may be time to pay, etc etc.
Ah ha may pickup on those not accepted or "banned" from Adsense, as i doubt that google will allow these to be shown on the same page as Adsense (competing text ads?) and i doubt that many will make the switch without a lot of thought.
If it is really a program for small publishers, (if its for large publishers only it's no great innovation), then its great to see... and if it succeeds and other follow as well, it may well reinforce that Google has really shaken up the online advertising market.