I signed up for a Knownhost VPS back in early Feb 2011. It has been a bumpy ride at times, but overall I am pleased with their service.
I can only recall one severe outage that lasted maybe half a day, and it was the data center's fault, not Knownhost's.
My site is Wordpress-based and has ~2,000 posts and a minimal of plugins. Traffic is at a couple of thousands visitors per day. I originally signed up for a VPS-2 package.
I had to open quite a few tickets, mostly about slow connections and slow loading times. Much of the time I was told I needed to "contact my developer to optimize my code." Even so, they would do what they could to tweak a setting, and things would speed up.
Disabling plugs didn't help, using a caching plugin didn't help, optimizing the code didn't help.
A couple of times, when the slowdowns were persistent and frequent, I researched alternative hosting companies, but stuck with Knownhost.
A few times I asked if upgrading the server would help. I was told I was not using anywhere near my allocated resources.
At one point I upgrade to a Litespeed add-on.
This past summer, the slowdowns were intolerable. One tech looked into it and told me the slowdowns were caused by PHP crashing. It's not that my code was not optimized, but my site was too large and/or too busy and kept maxing-out the RAM allocated to my node.
The tech recommended I consider adding more RAM to my package. After thinking things over, I upgraded from a VPS-2 package to a SSD-2 package. The SSD package had double the ram, less hard drive space, and would also potentially provide a performance benefit since Wordpress is very heavily database-dependent.
That was more than 3 months ago, and I have not experienced any slowdown at all.
In hindsight, I wish that Knownhost tried to upsell me into throwing money at the problem sooner, because that's what worked.
I'm not sure why it wasn't obvious sooner that I needed to upgrade my RAM, but it doesn't really matter.
Ticket response time is typically great, and quality of customer service is exceptionally good. They were patient, and walked me through anything I asked (so I wouldn't have to create a ticket every time the Litespeed plugin needed to be updated, and things like that).
I have been with Knownhost for 33 months now, and although there were times I was looking to switch to a faster host, I currently feel absolutely and completely satisfied with their service.