astrobiologist - 11:08 am on Apr 26, 2010 (gmt 0)
Very interesting statistics. And the causative effect in the gradual lowering of Adsense income (for a given amount of traffic) is, as has been pointed out, surely not the switch to non-IE browsers but the increasing savviness of users. To put it another way, we'd still be experiencing the same reduction in income per visitor even if there was no choice of browser beyond IE. It's just that a high proportion of people who don't tend to click on ads also tend to be selective about their browser.
Anyhow, as you say, not a lot we can do except to grow our sites to compensate for the downturn.