Thanks for the input guys. I'll research what Don was talking about as it looks like there is a very good example of it from Mike.
My explanation of the second option was a little wayward. Essentially I was thining of extracting all of the users with their home directory and profile path information from AD and building indivifual lists for each server that is to be migrated. Using that list of usernames I could then look to do the larger sites in batches.
I'm guessing thats what the passthru parameter is for?
Lots of information here for me to get my head around. I think I need to start spending a bit more time with Powershell. Really appreciate the assistance