Adsense – It’s Not Pure Traffic

Over the last few months I’ve been running adsense on a wide variety of sites with varying degrees of success. I have been using adsense since the program first launched, but I’ve been using it on a wider variety of sites over the last few months.
One thing I have noticed is that although higher levels of traffic help it is not the deciding factor.
Has anyone else noticed similar trends?
A possible explanation is the topics themselves which give higher payouts per keyword.. but even then that would not explain the overall results, as I don’t have any sites or pages that lend themselves to the really high paying keywords
Things I have noticed:
Forums do not pay out as well as normal pages
Blending pays dividends
Adsense for search does not work (at least for me)
Text links are more popular than I would have thought even when it is blatantly obvious that they are not part of the site’s navigation
The competitive filter may take hours to update