I know many people who have cable internet and DSL internet. I have yet to hear a horror story about a cable install, but I've heard MANY with DSL.
Example: about a year and a half ago, this girl I was dating wanted high-speed internet, but lived in an apartment and didn't have a cable outlet in the room she was in, and didn't want a cable strung through the house. She DID have a phone outlet, and insisted on DSL. So, she calls PacBell (now SBC) and schedules an appointment.
The installer comes out at 9am, and proceeds to spend the next 13 hours trying to get the thing working. The morons at the home office had mis-configured things at least twice, and each time he had to get on his cell phone and call a support number, which required him to wait 2-3 hours on hold before he could get someone. HELLO! This is the frickin PHONE company, and they don't even have proper phone support for their INTERNAL employees!
Anyway, they finally got it working, but due to the distance to the DSLAM, speeds were slower. A couple months later, it started flaking out, and she calls again. They're having problems with some of their equipment, and aren't sure when they're going to have it fixed, but it should be "soon." Two weeks go by, and the connection is still spotty. Keep in mind this apartment was only about 10 years old, so it wasn't like the wiring was ancient in the area.
So, she tries to cancel, and after waiting on hold for over an hour, is finally told that she signed a contract and that they're going to bill her for the rest of the year, but they MAY be able to pro-rate her bill due to the problems. After another hour of escalating, a supervisor finally agrees to terminate the service and the contract.
She called the cable company. They came out 3 days later, ran a new line where she wanted it (no charge; covered by the installation), and had her set up and online in 15 minutes. Speeds were faster and no outages.
Obviously, some companies can get good DSL service to their customers. Clearly, PacBell/SBC is NOT one of them.
I've had my cable modem since '97, and in that time, have only had about 6-10 outages, the longest one being 4 days when @home went out of business and folks were switched over to AT&T's network. All other outages were only minutes to a few hours long.
If you have cable in your area, I recommend it over DSL everytime.
-Troy