My family uses Skype.
We have local only at home, and we rarely use long distance. We use Skype to talk to relatives in Mexico, as it is way cheaper then anything else out there.
Vonage looks good if you use long distance a lot, and their international isn't that bad either.
All that matters for Skype and our DSL is that sometimes (mostly Sunday nights) you get some lag and echo, since so many people are using it.
Mario