Yes i've noticed they pay a lot less. I guess because its more of a task to get someone to click a text link than an image link.
Google optimises based on predicted # of clicks. So if you get one click every 100 impressions, you'd be better off taking 1 cent per impression than 99 cents per click. Google knows this and automates.
I changing now also to text and see how this is woking out for me. I had always image ads on my website and got a lot of 0.30€-0.4€ per click. I will post back how text ads are performing on my website. And is google ads paying for impressions like BobbySteel say i read always that google pays only for clicks not for impressions?
I don't seem to get less for Google image ads, but I only use them for top leaderboard spot. The text ads are placed in the main text portion of the page, and do well.
The weird thing is that it doesn't matter for me . Both (image and text) got a CPC of +- 0,02 a click. More flash (400% more per click) and Rich media (1250% more per click) would be much better for me but i don't get them that often .