I have run Beryl for months and have seen many huge and nice improvements.
I switched to Beryl soon after the fork from Compiz. At the time, I was on Ubuntu Breezy. The reason of my switch was a major issue with Compiz, making it impossible for my laptop to hibernate. Beryl did it. I could have solved it by myself, maybe, but didn’t have time to dig out desktop things.
Today, it is again some bugs that pushed me to switch back from Beryl to Compiz.