I don’t use them personally as I have the perfect host in the UK, but I recommend them to my clients on the other side of the pond. I’ve got plenty of clients who use A2 and they’re very happy.
I’ve just moved a number of sites to A2 because UK2, who’ve hosted most of my sites for years, started charging an arm and a leg for email accounts and also they charge for SSL certificates. A2’s support is very good and their prices are good, too.