Deadpool is a Canadian/insane version of Spider-Man. They both crack jokes (though I'm starting to dislike how Deadpool's jokes rely so much on the Internetz and 4th Wall breaking) and have pretty similar costumes. Obviously there's people who want to see them in a team-up.
I do like to see the occasional team-up from time to time but I'm not really a fan of the association. I'll certainly read the upcoming mini though, hopefully it grows on me.