So I'm looking at Microsoft's BPOS and pricing: It starts at $10 per user per month with a minimum of 5 seats, taking account of an exchange rate of 1 U.S. dollar = 0.64230201 British pounds (at 28/072010) that's £6.42 a month but a minimum of 5 means that the least that can be charged is £32.10 a month for the Standard Suite. That's £385.20 a year for the minimum number of users (5).
Then I looked at Google Apps, they charge £33 a year a user.
Already it looks like Google are cheaper at £33 as apposed to £77.04 for a years subscription.
But that there minimum user thing is a kicker. If we look at a like-for-like of 5 users then the difference is £165 for Google Apps and £385.20 for Microsoft BPOS. That's a £220.20 saving!
It's not a totally fair comparison though as the offering are different. With Microsoft there does seem to be many more whistles and bells though you're limited to using it with Internet Explorer or FifeFox (> 3.0)... there are also stipulated system requirements which might make a difference to some organisations.
It also links in with other Microsoft products, which can be either good or bad depending upon how you feel about it I guess, it'll certainly make a difference when it comes to upgrading software on the User's machines though. Whereas all that seems to be required with the Google Apps is to have a browser (though using IE6 might be an issue).
With the drive to do more with less at the forefront of most organisations' thinking it'll be interesting to discover who does best. The expensive security blanket offered by Microsoft is a definite choice but Google Apps is getting to be more and more mature and there are more and more things that can be done with it. It seems to be a much more innovative approach, and certainly closer to the ideal of cloud based applications.