One thing that's been incredibly difficult about the purging is that a huge part of the clutter is schoolwork and toys. I have a file folder box for each kid where I keep some key examples by year. I am very, very good at deciding which projects to keep. The kids, however, think that I must keep every worksheet and drawing they've ever done because they put their heart and soul into every single mark they make on paper. I've learned the hard way not to ever let them see me getting rid of their papers. "Oh, how did that get into the recycling? The cat must have knocked it in there! Let me get that out of there!" Once they go to school I can sort the papers and they'll never miss what goes.
And the toys. Oh, the toys. The boys have been big on video games this summer (it's really hot outside and I hate being hot, so send the parenting police on over, I will laugh in their faces) but they still do play Legos and Imaginext frequently. Everything else just sits around the house. If I suggest that maybe they could give those toys away to some kid who'd play with it they freak out. So again, there's going to be some culling done in a gradual fashion so they won't notice the toys leaving.
The clutter that is my fault: craft stash, books, magazines and clothing (fits now, will fit on the way up and down if I have another baby and full fledged maternity) is going to be harder to pare down. If anyone has any helpful solutions that aren't hiring someone to do it for me, please share!
The lesson learned from all of this -- just play with the kids and maintain the house over the summer. I will never again try to do any sort of house project when all three of them are home! For the record, we actually did all sorts of awesome things this summer, with Sea World and VBS and museums and tons of trips to the library.