it is kewl, I suppose...
a few thoughts that occured to me were...
If a mate of mine brought around a portable hard drive and said to me "I want to plug this into your system, there's just one little .reg file I need to double click on to make it work" my answer would most likely be "no"
You would ask first wouldn't you?
if you were doing this to use MC in public places, work perhaps? in the unlikely event that you were able to import a reg file, you would want to be 200% sure that nothing of personal value to you is caught in that reg file.
then there's liscensing issues to consider...
in fact, the more I think about it, the more scared I become.
Why not try something like:
install MC on each PC you would use it on. put all your music onto your external drive, and keep a library backup there too. make sure that drive is always recognised by the same letter on each machine, aim high up the alphabet, but not too high, mapped drives get named from z-a by default, so to avoid clashing with any of those, think maybe P:\ or O:\
when arriving at the pc, just load the library from the backup on the external drive, and then, god-willing, everything should be hooked up.
would that not do for you?