Blair Witch Short Films
I can't remember where I first saw this idea, but I've always liked it. The concept has your guests video taping themselves in Blair Witch form while they confess their wrong doings or anxiety over an everyday issue. Ask guests to keep the short films to under one minute (30 seconds is probably best). You'll watch all the films together at the party.
You can either:
a) have guests create their films before hand and have them submit the films to you before the day of your party or when they arrive to your house for the party, or
b) Have a video camera available at the party. Ask your guests to take the camera into different parts of the house/outside to film their piece. Tell them you'll be screening at a particular time and even offer prizes for the best short clip.