Here in Atlanta, we initially signed up via online chat, but I don't think it matters either way.
I'd say to go for it, even though I'd never do Comcast video, only HSI. I really wish AT&T would get their IP game in gear with U-verse; everyone that I've talked to who has U-verse for Internet does not like it.
Xfinity Internet is contract-free and rarely goes down for us. Then again, when we got it at the house, they installed a new line from the pedestal to the demarcation point, so your wire's mileage may vary.