I actually went to USC for undergrad... The string people are pretty strong and get their students to postdoc positions. Johnson is an interesting fellow to say the least. He does a lot of stuff on the side like "The Universe" on History Channel or even movies on his own. He has his own blog as well http://www.asymptotia.com
For the uni, if you are not a theorist there are very little options and some of the options are bad IMO. On the string theory side of things, there is a lot of separation among the people that do it. There is a clear divide between the more stringy people and more timey people. I would recommend it for variety, but then again you have consider what you want to do. String theory is also a lot of hot steam at times and telling you how much your ideas are crap.
If you need any more info just shoot me a msg.