I was an early adopter.
I've had Vonage since October of 2003.
I WILL NEVER HAVE A CONVENTIONAL LANDLINE AGAIN!!!
I've used it with three different providers. Comcast (1.5mb/256k), Charter (265k/128k), and Wave (3.0mb/512). The only one I had issues with was the Charter 256k connection due to bandwidth issues; talking on the phone and surfing at the same time could be annoying (chopping due to packets fighting). On my current 3.0mb pipe, I've never had a problem, Even with heavy downloading (Talked to my mom while I had a Linux distro downloading @450k/sec. Had to kill time somehow...)
Their customer service rocks! When I first got it, I was having trouble trying to get MCI to hand over my phone #. MCI sat on it for two months and wouldn't release it, tried telling me it was Vonage's fault. A three way call with Vonage customer service to MCI helped me to tell MCI where to stick it. Had my number in a matter of hours.
Overall I couldn't be happier. It's cheap (I chuckle out-loud at phone commercials now.), reliable, and neither I or the people I'm talking to can tell it's VOIP.
If you want, PM me. I'll give you a call.