Although this webinar comes from the UK it provides a pretty good overview of what BPOS is and how resellers can go about incorporating it into their suite of products. You’ll find the download at:

https://msevents.microsoft.com/CUI/WebCastRegistrationConfirmation.aspx?culture=en-GB&RegistrationID=1304293125&Validate=false

it runs for about an hour and is particularly worthwhile if you are considering Microsoft Business Online Productivity Suite (BPOS).