Sorry for reviving a somewhat older thread ( a month old ) ... but when you say the Google affiliate program, you are referring to using adsense as a source of revenue for your websites?
Or, are you referring to the recently launched (beta) Adsense/Adwords affiliate program where one gets compensated for referring publishers and/or advertisers to Google's advertising products.
I presume you're wondering whether Adsense is the best affiliate in terms of being a publisher... well, the biggest advantage is that Adsense does most of the work for you - contextually relevant, geo-targeted multilingual ads all served up and dynamically adjusted based on xxxxx metrics.
If you have a niche site, and feel you can target and manage your own affiliate advertising relationships, then programs such as Commission Junction and Linkshare are good options.
We work with all of 'em, mix and match depending on the site and content.
Cheers,
Rob