I've always wanted to do this...
As with most things this could go one of two ways... (1) someone is going to get hurt almost immediately, ending all the fun I imagined there would be, or (2) this is going to provide hours and hours of fun with little to no tears or fighting.
I don't want to jinx it... but so far they're still at it and having a blast. They've even upped their game and started jumping directly from the stairs to the mattress and bypassing the slide.
I was going to have the trash people pick up the mattress on Tuesday, but now I'm considering moving this set up to the basement stairs and keeping it all winter long!