I have been wondering this too. The only thing I have come up with so far is making a cute little booklet in Microsoft Word. I like to scrapbook and do crafty stuff, so I'll probably do something unique with it.
I've been working on it, and I've got interactive stuff the guests will have to write in like "Favorite memory with bride and/or groom", "what one item would you want to have if stranded on a deserted island", and "what advice do you have for the couple to have a happy marriage". I am hoping all my guests will participate and then I can take them up before the dinner/mixer and read them to everyone. There will only be 18-20 guests so it won't take too long. I think it will be neat to see what everyone would bring to the island like chapstick over a boat and xbox over a plane, etc...Who knows...it's probably not the best idea, but I am sure MY guests will like it.
If you didn't want to do a small booklet you could always include a small strip of paper in your oot bag, etc... with the stranded island question or the marriage advice.
hope that helps!