I know I'm breaking the rules of this thread talking about stuff like this instead of flight and tracking information, but hopefully ya'll will forgive me this one transgression.
If you want to migrate a user from your old machine to your new machine and you have already created that user on the new machine you can do it this way:
Create another user on the new machine (System Preferences->Accounts)
Make sure the new user is an Admin on the machine
Log into the new user account on the new machine
Delete the user name you originally created on the new machine
Run Migration Assistant and migrate over the user
It actually takes a lot less time to perform these steps than it does to read about them so if anyone finds themselves in this position it's a relatively quick and easy thing to work around.
Omg, an on topic post that's actually about Mac OS and not random flights!
I know I can create a new user...I prefer not to since minor random junk from that user might be left around after I delete it. Don't want to have to worry about stuff like overlapping UIDs either, since I have some non-standard UIDs for things installed from Fink, etc. So a straight-up re-install, migration (leaving out my biggest folders, those being my 90GB ~/Pictures and 20GB ~/Music), then copying those folders over manually so I can use my machine while that happens...
For most people who aren't digging into the Unix layer, though, what you said should work just fine.