well people sign up for different genres they enjoy, mystery, sci fi, suspense etc. (multiple is ok too) write a list of their 5 favorite books, to give their partner a good idea of what they really like. and instead of a wish list, they write a list of a bunch of (or all ) the books they've read.
then the partner picks a book (or books) in that genre that they really loved, as long as it's not on the list, and sends it to them.
the idea is to try and read something you new wouldn't try otherwise, but still in the realm of something you would enjoy.
and oh i would totally do a pet swap. that sounds awesome too!!! you could include pictures and maybe some people could draw their pets as well.