I posted about this a few months ago but we re-tested image ads out and was suprised to see them performing much better then when they first came out.
We always advocated text only but lately it seems Google image ads have made substantial gains. Our CTR went up nicely and our overall earnings increased 8%. Not a monster gain but worth it.
If you tried image ads in the past and turned them off I say give it a try folks, you may be suprised!