A customer of mine asked me if they could turn the trial version of FIM 2010 into a valid version if and when they decided to move on from a Proof of Concept workshop.
Now, during installation of the trial version, you are not presented with the option to enter a product key nor is there anywhere that you can enter a product key after installation (not that I've found anyway). I asked my "colleagues" in the forum the question and they provided some good answers. Simultaneously, I asked through my channels at Microsoft and got an answer that hopefully you'll found useful as well.
The Microsoft answer was: "There are two components which will timeout, the FIM Synchronization Service and FIM Certificate Management. The key is in included in the installation so you move from Eval to VL is by uninstalling Eval and install VL media. The configuration is stored in the database(s) so you do not lose any information in the upgrade. As usual, take a backup before you start and make sure you have a copy of the encryption keys for Sync."
See the thread in the forum here - http://social.technet.microsoft.com/Forums/en-US/ilm2/thread/b0764edf-95ff-4b4a-89a9-47ef4dce9d45
So go ahead, make appropriate backups of data and encryption keys and turn your trial into the real deal after purchasing a valid license.
I did this in our environment this evening and now I'll have to wait for 158 days to see if there is a hidden "gem" in the FIM Portal that someone didn't tell me about. I'll post an update if there are any news in the matter.