I bought this Mustang back in April of 2008 for $3,800 with a straight-6 and an overheating problem. The car looked to be in good shape but you don't really know until it's disassembled.
Last week I did exactly that. I took the car apart completely minus the new parts I had been installing over the months. I was happy to find very little rust, and none in the spots they are notorious for.
The window sills were the parts I was most anxious about. Floors are an easy repair because they can take simple bends or flat pieces to repair. Building window sills is a little bit more involved.
I guess they are right, California cars are usually the cleanest when it comes to rust!