This past weekend I set up a small business on Google Apps Enterprise. They had already gotten their domain, along with hosting for their website. So I had them log me into the interface for it, changed teh MX records, and bingo.
Damn, is it ever easy. I can't see why a small to medium-sized business would possibly want to do an Exchange server (which sadly, my company did and I am responsible for).
Not only that, but there's a free version that has the same limitations as regular GMail, yet allows you to use your own domain. So if you've got one (I do) you can have your own e-mail, yet residing on GMail's servers and thus having all those features. Really cool.
This explains all the snow in the south east.