This thread [webmasterworld.com] may be of interest.
It suprised me, but this is also true for the content ads I run.
On average, my image ads are roughly 2x-3x above the text ads in CTR and conversion % is about the same.
If you haven't added some nice image ads to your campaigns running content network, give it a try.
Text ads .01% CTR
Image ads .40% CTR
I've implemented graphic ads on about 1/3 of my products - I've seen a significant life in volume (average 6% more clicks - clicks I wouldn't have seen otherwise) best being 15% lift. The jury is out on if these are quality - converters yet. But my stats show no decline in conversion rates.
M