Until support for custom MX records is supported the service is really not useful to the bulk of established small businesses. We already have our hosting solutions and online stores etc. While those services are nice from Office Live it's not practical to expect us to drop our current solutions and run here.
Now the online sharing stuff, there is some real value. That along with the Outlook and Office Conectivity is excellent. Until you let me set our own mx records for domains there is very little real use value, just a great idea and excellent tools that we really can't use in our daily business life.
Please get the custom MX support added to the offering! Until then the best service available (becasue of IMAP, POP3, SMTP, Mobile Connectivity....) is Google Apps.
Thanks!