Well... in almost 7 months with Hostgator I only noticed one downtime (which was caught by siteuptime, not by me) and that was during a DDOS attack. I'm not saying that they had no downtime during this period (servers need to be restarted from time to time), but the downtimes must've been short and very far between.
I contacted support a few times, but not because I really needed it. By email I received a response in under 5 minutes. By IM... well... pretty fast. Not instant (which would be impossible anyway), but 15-30 seconds at most. I'm very satisfied with the service.