Yahoo! has a service called Yahoo! Small Business that sells domain names at a very attractive price. If you think of registering a domain through them, read on. And maybe also have a look at what others say.
First Yahoo! is not an accredited domain registrar, but simply a reseller for the Australian domain registrar Melbourne IT. If you ever have a problem with you domain registration however, you'll have to deal with Yahoo!, and their support is appalling to an extent I have never met before. They consistently and repeatedly reply to emails with irrelevant pre-made messages: this did not happen to me once or twice, but about fifteen times.
Given my first experience with their support staff, I rushed to transfer my domain to another registrar as soon as the 60-day no-transfer period after registration was over. The transfer was systematically denied. Whenever I got a human to reply, their answer showed a striking ignorance of .com transfer procedures, replying with transfer requirement only applicable to other types of domains (.info,…).
After three days, I ended up calling them and I was told that they could not do anything and referred me to Melbourne IT. Emailing and calling Autralia several times, I was told that I had to deal with the reseller (Yahoo!) directly.