Here's one more small criticism: most people make ssh all caps or all lowercase.
Another thing you might do with your script is verify that permissions are correctly set on the .ssh directory and the authorized_keys file. Maybe add a usage message. Toss it into the Code Catacombs. Or even better, poke around there. I'm sure you're not the first person to do this. It's interesting to see how other people code programs to do the same thing, in terms of style, documentation and cool tricks. Reading the code of others critically is a great way to learn, and is one reason that I love PM.
Cheers and good luck with your programming.