Not sure if it’s Cairo’s or GTK’s fault, or anything else’s, but it looks quite bad.
On the good news front, I have to say I didn’t feel it being much slower than 2.6. Of course, as I said, I didn’t do any performance tests, but still, doing normal desktop tasks, I didn’t see it perform too bad compared to 2.6 (which is not slow and unresponsive, despite what Eugenia might say). To show a little example, here is the color selector dialog with no Cairo:
And the one with Cairo:
Which one looks better?