Thanks for the insights in this thread... They've inspired me to actually do some testing myself
I guess I've been a bit complacent with a 30% CTR and not thought about trying to optimise things any further but I'm going to start today
I've looked back over the last 30 days of data and found that text ads have performed 55% better than image and rich media ads combined so I've fucked them off.
I've also set up a basic split test to see if my assumptions were right about font colour that I'm going to run today.
I've always used a single large ad block between the h1 and first paragraph aligned to the left of the page, but after this first split test I'm also going to try the double block as suggested above.
Out of interest, for those of you split testing, how much data do you normally wait for before moving on to a new test?
I'll post my results in case anyone's interested
Cheers