A new topic was published to MSDN that shows the end-to-end process for creating a custom logging activity in Forefront Identity Manager 2010 (FIM 2010).
How to: Create a Custom Logging Activity
The topic covers how to create a FIM custom activity in Visual Studio that logs information about a request to a file. The custom activity includes a user interface (UI) that allows you to specify the location and file name for the file. The UI will appear in the Workflow Designer when you create a new workflow in the FIM Portal. The topic also covers how to load an activity into FIM, configure the activity in FIM, and run the activity.
The following post on the FIM TechNet Forum links to the above topic and requests feedback and suggestions for additional examples: