I've started with one server in approx. 2003, in 2003/2004 they had once or twice half day downtimes, I can't remember any downtime since 2006 at least, sometimes certain routes are a bit slowed down, but I guess that's to be expected (they nicely inform about stuff like that in the forum) Oh yeah in 2009 they moved data centers which resulted in 6 hours scheduled downtime during the night.
I've just seen nowadays they guarantee 99% Network availability.
None of my 7 servers has ever suffered a hard disk crash or similar, which is nice but not actually a meaningful data point. (Another nice point, internal traffic is free, even between their data centers)
Their support is top notch in my experience, answers within 15 minutes with the free support. Just read a random post in their support forum, they switched a defective power supply within 2 hours. They once phoned me because one of my servers was behaving suspiciously.