This is another article that I've wrote for the Service Manager Product team showing how to work with the Service Manager Powershell cmdlet to create a customization within Service Manager 2010.
The initial problem is how to surface up the contained activity details to the change request level. This makes it easier to format/send notifications and such things. I've wrote a blog post about this solution which uses the SMLets PowerShell module (a CodePlex solution) to get the activity and update the parent change request description.
The overall solution is using custom activity class, custom workflow, using the Service Manager Authoring Tool and the Powershell Cmdlet SMLets from Codeplex.