I'm sorry I can't offer any input on their services as I've never hosted any of my sites with Yahoo - with these companies the proof usually comes with their customer support. They promise the moon but when you run into trouble are suddenly scarce - not saying it happens with Yahoo, because I don't know, but I am aware of other hosting companies who are notorious for bad, or nonexistent, service when it gets right down to it.
It's incredibly easy to offer a great hosting package with tons of space and lots of email addresses, etc. - our
member hosting package is a fine example of that, I think (although at this time we do not offer a website builder). But if there's no one to help you when your site is mucked up those extra features aren't very comforting.
I'd just suggest checking to see how fast their response time is, also look online for "
Yahoo hosting reviews" or whatever the name is of the product they're offering to see what other people are saying (and I'd suggest doing that for anything like this, actually.)
I hope that helps - maybe someone who hosts with them can jump in here with some thoughts on the matter!