I like C# and all, but at the current price point, I don't think it's very interesting. $500 for the development kit, $199 for the module. If you need the 32-bit performance (it uses an ARM chip), then it might be more interesting.
I should also note that the Javelin stamp (which runs a Java subset) is about $80 in quantity.
None of these are cheap enough for my next holiday lighting project.