We have it and really like it. The features are great, especially for the price - particularly when you compare the same with the phone company!!
We just recently added a second number so that DH's mom can call us on a number that is local for her in the LA area, and it just costs us a little bit extra in a month.
The local/long distance charge from Vonage is cheaper than basic service for our land line. We'd drop the land line if we could, but we need to have it in order to get DSL service from the phone company (how lame is that, we even pay for business class DSL, and they still make us pay $40 a month for phone service

). If we didn't live out in the sticks and could get cable service, we'd drop the DSL and get a cable modem, cutting the phone company out altogether.
The one problem is that our power here is questionable (we've got dirty power for some reason, and the electric co-op can't seem to fix it), so we sometimes lose our broadband service, and therefore our phone. Most of the time, though, we just need to reboot our broadband router and that fixes it. The nice thing is that if our phone isn't available, any calls are redirected to DH's cellphone. He also gets an email when we get a VM.
For a while, we had problems with feedback/echos/bad connections, but DH changed the setting on the Vonage site for the broadband speed, and that made a big difference.