Had them for years at my parents house, and then for a few months at my apartment. I'm sure it varies by location, but this was in two entirely different cities for my experience.
Parents house: Had at least a years worth of 200+ms pings, even to servers less than 50mi away at most times during the day. Horrible download speeds. Network was severely overloaded. Down completely often. Even when it was working well, they always charged more for less speed than other cable companies around the area, but there was of course no alternative for HSI.
My apartment: No contract, internet only, $39.99 for 10/2. Took them 4 months of calling each month when my bill arrived to get them to credit my account for the $3/mo rent for a modem they never gave me. Was using my own, which I had to explain 4 times until they took action. Seemed to always lose connection for a couple hours real early in the morning on Sat or Sun, guessing for maintenance.
About 5 months into my service, speed automatically increases to 25/5. Couple months later, bill goes up $15. Call them and they explain prices have increased and extra speed was only promotional. In order to get my previous rate and speed, I must agree to 2 year contract. Canceled on the spot. Used tethered 3G from smartphone for ~3 months until I moved.
My condo luckily has Verizon FIOS. Had it about 9 months, not once has service been down. Speed is always above advertised and pings are great. Screw Charter.