I switched to art the other day (GPE conversion here). So far performance is still very good, battery still very good, maybe a little better. There is a pretty comprehensive list somewhere that says what apps are compatible or not. I went through and made sure my core apps were compatible and then flipped the switch. So far I haven't run into any compatibility issues. From what I understand is that Google will be using art in the next Android version so it would behoove developers to start making their apps compatible with art.
Edit:battery is noticeably better, although not by that much.
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