I've been working on it for about a week and a half to learn XNA. I have previously used DirectX and C++ so most of the concepts are familiar.
I'm finding XNA is a really nice library to code against compared to DirectX. Things like Mouse.GetState() and Keyboard.GetState() just make sense. Its many, many more lines of code with DirectX to get the same result.
Heres a couple of screenshots


Download the demo (Version 1)
The demo features a randomly generated map with 10 coins to pick up.
Controls:
Jump: Right-mouse or 'A' button
Move around: WASD or left thumbstick
Look around: Mouse or right thumbstick