Once you get past the basic interface and deceptively bland logo, you'll notice that Thumbstacks is actually a pretty interesting application. Why? Because it fills the one remaining gap in the supposed Web 2.0 office suite that some bloggers are rooting for. From the site:
With Thumbstacks.com, you can make presentations - like slideshows, or outlines - right in your web browser. When you're done, you can share your presentations with anyone, anywhere, just by sending them a link. Want to see an example? Here's a presentation about us. It all runs right here, in your web browser. You can create your presentation, save it, modify it, update it, whatever - then click "publish" and you'll get a link you can use to share it with everyone. The best way to understand is to try it out!