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/

Microsoft recently upgraded the BPOS mailbox storage limit from 5GB to 25GB. While new users get the 25GB limit automatically, you need to manually upgrade your existing users to take advantage of the new limit. This short tutorial will show you how: http://www.screencast.com/t/NzM5NjEwZDEt

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