Before I went off and got a real job (hehe), we had been running servers (dedicated and VPS) since 1996. In that time, I found one other host that is even comparable to Knownhost. The other guys were great and I hated to leave them, but their prices kept increasing due to the datacenter cost, and I just couldn't justify the prices anymore...sadly.
After a few years of jumping around to various hosts, and some really bad experiences, we found KH. I honestly don't think we'll be leaving here, unless we need another dedicated or two, and even then, we'll probably keep a VPS here.
The only downtime I experienced was a few minutes here and there due to packet loss/routing issues at the datacenter in CA. I don't think the server itself has ever been down. At one point, we had 180+ days straight of uptime, but had to restart the VPS after an update. Would have been fun to see how long she would have gone.
I don't use Support often, but when I do, Support is very fast and very good. Honestly can't find a single thing to complain about here.