I first discovered this at laurie beggin glass musings where she installed an interactive guest book.
Have you seen Slide sliding around the internet? It's a lot of fun to use to make your blog more interactive. Very easy to set up.
I've got a Slide slideshow at the bottom of my family's blog, The Adventures of Pam & Frank, where it chronicles a road trip to Seattle that we took this past summer. A Slide guest book is installed at the top of my Plate Diaries. I installed it recently and very quickly three visitors signed it. I know these people in real life (a very good friend I've known since 6th grade, my sister, and my favorite former neighbor who has stayed in touch for the past 8 years.) What I absolutely love is that while none of these wonderful ladies leave comments on any of my 4 public blogs, they signed my guest book. I had no idea they even read my blogs!
Here's my guest book.
Setting up and installing your Slide is so darned easy I'm not even going to give you a tutorial. You don't need one.
Now put your thinking cap on and imagine how you can use Slide to promote your site or product. If you comment here with your idea you get a gold star (figuratively) and everyone will learn what a brilliant thinker you are.
Go forth and slide! Leave a comment here with a link to where you put your Slide and we'll go check it out!