Here's the first provider that I have found that is offering the Office Web Apps in a SaaS model.  In this case its Access Services only in a service tailored to help enterprises move their legacy Access DB's and Access applications into the cloud.  This includes conversion of legacy VBA code into Access Services supported macros which can run in the cloud!

There's also some new features in Access 2010 that improve performance when run atop of SharePoint Server 2010.  Check it out the links below for more information -

Check out http://www.accesshosting.com and http://www.access2010converter.com/ for more information. 

Here's a link to a number of video tutorials on using Access Services http://accesshosting.blip.tv/

Here's one on field validation that I found particularly interesting with Access web databases.

If you're not already familiar with the Office Web Apps for SharePoint 2010 (Word Services and PowerPoint Services are available in SharePoint Foundation and with SharePoint Server you add Access Services, Visio Services, OneNote Services, Excel Services) here's a several good links

Office Web Apps - end user focused content http://blogs.msdn.com/b/officewebapps/

Office Web Apps - technical content on deployment http://technet.microsoft.com/en-us/library/ff431687.aspx

Office Web Apps - technical content on management http://technet.microsoft.com/en-us/library/ee837419.aspx

So you're probably asking yourself how this related to BPOS? Well in a few ways.  First, with the new release of BPOS being released by Microsoft within the next 6 months or you will have access to the Office Web Apps via your SharePoint Online site collections.  Now we're not sure of all the details or cost information at this point, but it will be a very powerful BPOS feature.  I can't list all the ways having the Word Services or PowerPoint Services would make it easier to modify an SOW document on the fly or present a PPTX right from the web! Second, because BPOS will now embed these services right in your SharePoint Online sites you should be preparing yourself for how you're going to leverage this foundation to build your own solutions.  For example, you could potentially convert legacy Microsoft Access applications to cloud-based databases (helpful tool to do just that).  If you're in a large organization you probably have 50-100 critical access DB's.  In SharePoint you get the scale and power of SQL Server with the UI and Access desktop client integration all in a web interface that your Access DB end users can easily access.  Pretty powerful.

Off the topic of BPOS and onto SharePoint 2010.  Found this great link today on configuring remote PowerShell. So I thought I'd share.

http://blogs.msdn.com/b/varun_malhotra/archive/2010/06/10/configure-power-shell-for-remote-use-of-sp-2010.aspx