I was 100% up and running with Vonage as of August 17. This was about fifteen business days after they had requested a transfer of my existing land line from BellSouth.
Quality is superb--I can't tell a difference from the old land line. Callers see nothing different. They call the old number and talk to us. The voicemail works very well and emails the messages as an attachment if I so desire. Good stuff.
A potential downside to home VoIP is a problem with devices that need to make electronic calls out, such as Tivo/DirecTV and the like. There's a site here that talks about using the wiring in your house for VoIP, but I haven't tried it yet. The Series 2 machines for DirecTivo don't really require a callout, but they will send you the nag screen every day if you don't do it. There's supposed to a be a hack that allows the machine to use a wireless LAN to call home, and I might try that next.