I've been a user of mosso's for 2 years. And quite honestly I would not recommend them. They do some things well (availability of support, fast servers), and do others surprisingly bad: ill-informed support techs, really odd clustering problems like two authoritative ftp servers for one domain in one recent case that no one there seems to have a clue how to fix, and usage (hit based) metering.
I hope they fix the problems, but for now, I wouldn't recommend them.