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.

I'm in a similar boat to plusbryan. I would say that they're OK for basic, static site hosting. We use them for hosting free websites for some of our customers. Otherwise, S3 is still the gold standard. And since their costs are reasonable, why not just use the gold standard?