I've just started using them, so as far as downtime I can't comment.
What I will say is:
Their user cp is different than anything I have seen, not hard to work through
just a completely different set-up than lets say Hostmonster or Hostgator.
They have a help section that is very good but at the same time not thorough??
(Sounds funny, but that is how I see it)
I have been dealing a lot with their support and honestly so far they have been
fantastic!!
These guys know their product, and are understandable. I believe I have talked
to maybe 5 different support techs and all seemed to be located in the US (Kentucky)
Very easy to communicate with.
Wish I could say more about their performance, but just can't at the moment.
Good luck.