I have knick-knacks, and swag, and gifts, and pictures, and Dilbert cartoons, and books, and business cards, and drawings from my kids, and speakers for my MP3 player, and a radio/CD player, and an assortment of pens, and thank you notes, and "awards" from my site manager, and buttons / pins, and calendars, and plants ... and so on.
I'm not quite ready to test this out yet, but I think I will do this in the next month or two and see what really does happen. I think I will up the ante as well by clearing everything on a Saturday, when very few people are here. Then to go one step further I will add several of my "items" to other people's desks over the following few weeks ... and see if they notice them!
Doesn't that sound like a fun social experiment?