Google mail is a great way to run multiple domain addresses as it can reply from the address it was sent too, try that in Outlook!
One annoying problem for me is sometimes it "has difficulty" sending the email from your domain, maybe a timeout on the server or some other network issue. When this occurs Google will "kindly" forward your email using your gmail account instead. Now this sounds reasonable but it's annoying if you have your own business and you are effectively replying to...