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/ 

One of the powerful ways to leverage SharePoint and BPOS's SharePoint Online Standards is with Content Types.  SharePoint Content Types allow you to define a standard set of metadata about individual pieces of content.  In a given Document Library you can have many, many content types.  For example, you might have a library called Customer Documents and within that library you might have three content types - "Contracts"  "Project Documents" and "Time Sheets".  In the Contracts Content Type you would have a set of defined columns. Some of these columsn would be custom - such as "Customer Name" but others you'd pull directly from SharePoint Core Columns such as those having to do with mailing addresses.  As a part of every SharePoint site you should create the content types that you will use with your document libraries. This will allow you to enhance search, workflow, usability, findability and have create views that do the heavy lifting of manual foldering.

In BPOS to get started with content tpes you need to first go and ahead and see what Microsoft has built for you -  to do this go to Site Actions > Site Settings > Site Content Types.

Next - Click on any Content Type - as an example I have created "Proposals" - you probably will not see that option so choose Document. 

Explore the columns that make up the Content Type. Then add a new or add from existing. The next screen shot adds a new column.

Adding a new column is easy - I like to use Calculated Columns from time to time. I am going to use a Calculated Column because I want the "Customer" to display as an aggregate or combination of multiple columns.  This makes for easy viewing - I can combine multiple values into a single text string value.

Here's where I add my formula. The result of this formula will space with spaces "Company Phone Phone" in the Customer field throughout my list.

This is a nice summary - but to work with columns and Content Types you need practice.  Try making a view of your own with your BPOS SharePoint Online Standard sites.

More Reading:

http://msdn.microsoft.com/en-us/library/ms472236.aspx