I signed up on a friday afternoon and my account was setup in less than 3 hours. Support was great and transferred all my domains from my another host on the same night.
Support staff is great and even after the superhosting boom they are doing very well. Their forums are very active and Steven is always there to help.
The server load is very low most of the times after 2 months monitoring it (right now is 0.11). Speed is always good and the server never crashed. The uptime for april was 100% and march was 99.9%. All maintenance is previously informed via e-mail and forums.
Excellent features (RVSkin, Clientexec, etc.), great support (15 minute average) and the best uptime. Active public forum is a plus and uptime reports by third part is also great.
Site5 is doing an excellent job, I could not be happier.