I recently developed a 3D game using XNA and have posted the binary and source on www.threesixbox.com. The game's name is Snake and it can be found at http://www.threesixbox.com/project/ id=f580fc1536
I've been developing games since the early 80's but just downloaded XNA last week. During the course of the project I went through several iterations of optimizations and learned quite a bit about XNA.
I know that whenever I'm learning a new development language or library, working examples are very helpful to me. If nothing else, this project can be used as another source of information for anyone interested in XNA development.
Let me know what you think...