Matt Mason of Avatech Solutions pointed out a few important items related to the preceding post on replaying a journal file:

One topic that you did not cover – using the journal file with Revit external commands.

Here are some things that I've noticed in the past:

If your external command has dialog boxes, your application will freeze if Revit is being driven by a journal.
The alternative to this is to use the JournalData StringStringMap in the ExternalCommandData which is passed to you.
- You can read values from the StringStringMap and use them instead of your dialog boxes.
- You can write the values at the end of your command – based on what the user selected – so that your existing commands can be played back.
When last I looked at it (2009?) there were problems playing back your command if it included calls to select elements using PickOne or WindowSelect.

Thank you Matt for these valuable hints!

A Solar Radiation Technology Preview for Revit is now available on the Autodesk Labs site. Scott Sheppard provides some additional background information on this as well.