Google Gesture Search is a unique app that serves as more of a future concept or tech demo than an actual integration into the Android software. The app's whole goal is to experiment with a new way to browse the content on your phone. Instead of typing or even vocalizing your search, you can now write the search on your touch screen.
So let's say I was looking for a certain application out of the hundreds I have installed on my device. I can write the first letter of its name and continue to write letters until it appears on the screen. This is a very useful tool for anyone annoyed with the need to use a keyboard. While it does provide a new experience and way to browse, it still isn't something that I personally believe to be practical. The process of writing letters on the screen still requires opening the app, writing however many letters it takes to narrow the selection, and tapping on the app.
This app could be useful if someone has a ridiculously large contact list but still the ability to utilize voice commands still trumps this app. It is available free in the Android Market so definitely try it out. It is pretty accurate and fun to use the first few times.