My family had a problem because you can only get two permanent plates in MD.
We had one on my mom's car, and one on my dad's.  Then when I started
driving, I needed one for my van (yes, I know I'm spoiled. ;)  It was a
really big hassle to get a hangtag for the third car when we already had two
plates.  So, while I see the advantages of permanent plates, they can be a
problem too.

Also, you might want to see what kind of program your state has set up for
enforcement.  My parents will call the police and report a license number
when a car is illegally parked.  More than once, we've come back to find
tickets on that car.  Might be vindictive, but it sure feels good...

~Joy~