Just have to add that RackSpace are the best data center, period.
Expensive, yes, but it's worth the money and you can really offer 99.999% uptime. That's 100% minus the downtime needed for backing up data, and no one would complain about that.
Support? My God, those guys are just insane! If you're a host there, you can pass on all that to your clients. We wouldn't leave them for anything.