I have heard some of the same things you said about Vonage, but was going to try it out on one of my lines anyway. However, I got it home and discovered I couldn't get a local phone number.
I had also had a customer that had Vonage and had trouble running it through the same firewall I use.
A friend suggested I try Packet8. So I returned the Vonage and bought a Packet8. I've had it more than a year now and can't be more pleased.
I have had 2 or 3 occasions where I dialed a number and it failed, but a redial attempt worked each time. No one knows that I'm using an internet phone connection - it's clear as a bell.
However, I would never use one of these to replace a primary line. I want a phone line that will work in a power outage or when the internet is down.
DJG