I don't know if you guys go to Rogi's official forums, but from what I heard there, the people that sent him letters all got replies, and got a lot more stuff than they had originally expected too! One person mailed him asking for an autograph, and s/he got 2 hand-signed autographs and one preprinted postcard. Another person sent him a letter with 2 photos, which he signed, and along with other stuff that he/she didn't specify.
So, I decided to post his fan-mail address here as well, seeing that it is such a success.
You should put in an extra envelope with the right number of stamps in order to make life easier for him, but I think a person forgot about it, and Rogi still got his own envelope and stamps to return the mail. So, good luck everyone!