One of the greatest BPOS features is the quarterly updates - this suggests a more contemporary approach to on-going software development pioneered by Google.  Part of the power of BPOS is the regular updates that deal with issues and add functionality to improve the overall user experience.  With SharePoint 2010 launching in 1st or 2nd Q 2010, BPOS won't be far off in completing its migration to the new 2010 feature set.  We will be watching this migration, version upgrade very carefully and documenting anything an everything we find about what an end user or service administrator might need to do prior to and after the upgrade.  There might be something as simple as modifying the master page to include a new Terms and Conditions Reference, or a change / update to your existing workflows.  At this point, we don't have all the details but the list is starting to form.  Look for something in the coming months.