I am seeing image ads a lot more frequently now. I think there has been a big increase in showing image ads. They must be achieving a good CTR for Google to show them so much.
I've seen a couple on my sites lately, too. The ones I've seen have been brief advertising blitzes by big companies, but they've been mostly text ads otherwise.
I have also noticed an increase in image ads. I think this is good as it gives more options for publishers. Especially since you can request just image or just text ads.
Another reason that a mix of image and text ads is good is that it reduces ad-blindness for regular visitors. I always notice an increase in CTR when there's a mix of both.