I've had similar experiences with Packet8 (
http://www.packet8.net/). I've been using their VoIP service for 3 months now and mostly like it. Here's my story:
I needed a new phone number to use exclusively for business in my home and didn't want to pay the almost $40 per month the phone company wanted to charge (long distance is on top of that). Also, though I don't get reimbursed for business calls as much as I should, not paying for long distance appealed to me. VoIP seemed like a decent option for what I was looking for. I get a local phone number and don't pay any long distance, all for only $19.95 per month. Sure, there is no 911 service but I have a regular home phone as well as 3 cell phones in our family so no major loss there. The Packet 8 system is similar to Vonage - you get an adapter to plug into your switch and then you plug a regular phone into that.
After three months of extensive use, I find it to be mostly reliable. The call quality is good unless I'm uploading something or downloading a large file (I use cable). In a few cases I've had to use my home phone as a backup but 98% of the time it works fine. In May I spoke for over 5.5 hours total and didn't pay for any long distance. I'm probably saving around $45 a month over my phone company.
The only other downside has been some occassional downtime. Every once in a while (rarely) I pick the phone up and there is no dialtone, requiring me to hard-reset (power off) the Packet 8 adapter. A minor inconvenience, really.