I came across this great solution which can get you most of the way there with your public folder support for legacy SharePoint 2003 to Exchange Online migration scenarios.  It's from a company named MessageOps (http://www.messageops.com/software/sharepoint-bridge) and the product is called SharePoint Bridge.  What it effectively allows you to do is move messages from a designated Exchange Online mailbox into a SharePoint Online document library.  Check it out at the link above.

A frequent question I receive is how to monitor the availability of BPOS and how to access BPOS service notifications.   There's a few good techniques and resources out there.  In my experience, BPOS availability has been great and I've only had one issue since August 2008 when I started using it. It cleared up within a minute or two.  Here's a couple of good tips:

Monitoring BPOS

There's a few different ways to monitor your BPOS service.  If you own a monitoring tool such as Solar Winds' IPMonitor (http://www.solarwinds.com/products/ipmonitor/) you can easily configure fairly sophisticated queries against your various BPOS service URLs such as SharePoint sites or OWA.  I generally configure some alerts againsts my SharePoint sites and OWA.  In the use of your BPOS service you also rely on either your own DNS hosting infrastructure or perhaps a third parties.  I set up QoS monitoring on all my DNS servers - remember if DNS is not working properly mail flow, your website and other services may not function as you have designed.  You can also probably monitor SMTP by configuring a dedicated user (consuming a license) and using an SMTP monitoring rule that can be configured to support authentication (these are available in the IPMonitor product). 

BPOS Service Notifications

BPOS Service Notifications are another great way to keep in touch with Microsoft annouced service issues or maintenance. 

North America Microsoft Online Services Standard RSS Feed https://rss.microsoftonline.com/

APAC Microsoft Online Services Standard RSS Feed https://rss.apac.microsoftonline.com/

Europe Microsoft Online Services Standard RSS Feed https://rss.emea.microsoftonline.com/ 

Message Filtering RSS Feed http://rss.messaging.microsoft.com/ 

Developers should be getting ready for Sandboxed Solutions in BPOS SharePoint 2010. 

Here's some background:

One of the ways we can think about Sandboxed Solutions in relation to SharePoint 2007 is that they are very similar to 20 site administrator templates available in the Fab 40.  These were templates site administrators could simply upload and then use to create new sub-sites.  In SharePoint 2010 Sandboxed Solutions are actualy WSP's that site administrators can upload.  IT can centrally control what it decides site administrators can deploy and then carefully control how these solutions run and the resources they consume.  That makes them an attractive alternative to server side solutions that are deployed to a SharePoint web applications and activated as Features on Site Collections.  Because BPOS 2010 supports Sandboxed Solutions developers should be starting to think about -

1. How they design, develop and deploy if they are a developer internally at an organization
2. How they will design, develop, deploy, market and sell if they are an independent developer or an Microsoft ISV

Link for Developers on Sandboxed Solutions and BPOS SharePoint 2010

A good place to start is Channel 9 from Microsoft.  I highly recommend that you take a look at this link and watch / read the material referenced therein.

More to come on SharePoint 2010, BPOS and Sandboxed Solutions.

http://channel9.msdn.com/learn/courses/SharePoint2010Developer/SandboxedSolutions/