I was going to move to Vonage, but two things stopped me:

1. The insane amount of taxes - $9 of taxes on a $15 account (I didn't need the unlimited plan), and
2. Lack of support for my home security system, which meant that I still would have had to keep the most basic landline package.

I use Skype when I travel internationally on vacation, but only because I usually spring for Internet access once every other day at my hotel. The call quality is good, not great. I buy the minimum 3-month package with SkypeIn/SkypeOut/voicemail, and if I'm expecting a call after turning off the computer I use call forwarding to either my local cellphone or the hotel front desk. It is not the cheapest solution due to the 3-month minimum, but three weeks in Australia, being sick a bunch of the time and calling back to family, doctors, etc., still cost me less than $30 over the HSIA charges which I would incur anyway.