My sister has been using Skype for some time, and she's been reasonably happy with it. Most of her friends here in the States use Skype, too. Skype is good enough for most folks.
I've never been terribly keen on Skype. It worked on my Ubuntu laptop, but it seemed like a complete resource hog. Ultimately I decided not to use it for three main reasons:
- Skype is not Free Software.
- Skype uses a peer-to-peer mechanism to make every Skype user a relay point for Skype traffic
- Skype only talks to Skype
The third issue is a common problem with closed-source solutions: lock-in. Skype clients can only talk to other Skype clients, or to telephones via the SkypeOut service. There are lots of Voice-over-IP solutions being developed these days, so it seems rather short-sighted to lock oneself into a single vendor.
The Gizmo Project offers GNU/Linux, Mac, and Windows clients for their softphone. Gizmo softphones do not employ p2p routing. And most important of all, Gizmo softphones can speak SIP, which means it can work with other VoIP products and providers, like Ekiga, FreeWorldDialUp, Asterisk, and more.
Indeed, I was able to iniate a test call from Ekiga (the successor to GnomeMeeting). Ekiga is Free Software, and as such will be my softphone of choice.