I've been giving the first XNA lectures to students this week. This is actually a world first; the first time ever that XNA has been used to teach C# to first year students in Hull by a tall bloke who needs a haircut.
Anyhoo, it has gone pretty well. I had a few minutes spare at the end of the lecture so I showed the students "Hot Salad Death With Cheese". I've given them the source of the code and offered a bag of Walkers crisps as a prize for the person who produces the best game based on it. If you fancy a go you can pull the files down from here.