I've used Skype now for over a year. Great
I don't know what SkypeIn is but I do use SkypeOut. Loaded it up with $25 last year and have still got $6 left. Do not "out" for inland calls. But for Foreign call's it's sometimes 75% cheaper. I've called Brazil, India, China everywhere it's good. Even better if the client has Skype, then it's free. Conference calls are useful too.
I'm not sure if it would be a good idea for here though. There would be no posts, everyone would be Skypeing instead