For the most part, I've sent out what I felt were "safe" requests. I use the Sports Card Forum TTM Manager and I like to make sure that I send to those with a good history of signing. Sometimes you want an autograph enough that you just chance it.
I found "Mean" Gene Okerlund's address on another online site and while there were some returns entered, it had been awhile. The address obviously worked. This beauty came back in just eight days.