AdSense publishers who use referrals heavily will be happy to know that AdSense have added the ability to track referral results with channels. This has been a long time coming and something that I’ve heard quite a few complaints about.
URL channels don’t work so you’ll have to set up custom channels instead. This means going through your blogs and changing the referral unit’s code to do this but in my opinion it’s worth it if you’re running the same referral products on multiple blogs as you’ll be much better informed about what is and isn’t working.
More information at Have a track attack with new referral channels (Inside AdSense Blog)