Ok, it's not like it's all comics will be free that day. It's only certain ones (and generally ones I'm not terribly interested in) but they're FREE! To find out more check out http://www.freecomicbookday.com/ and to see a list of comics from the "gold sponsors" we have http://www.freecomicbookday.com/sponsors_gold.asp
Personally, if Silver Snail is restricting it to one per customer then I might forego my usual Marvel choice and go with the Conan/Star Wars book.
(teehee, the spell checker wanted to change "Conan" to "Cowman")
PS. The day in question is May 6th, in case you were wondering.