The .Net Micro Framework has been around for some time now (it's at version 4.1), and as with all things Microsoft it's really taking off post the V3 release.
Sadly the development boards for the Micro Framework have been fairly limited in their range and price (read expensive!), until recently with the release of the Netduino, a .Net version of the popular Arduino platform.
This fantastic board is idea for hobbyist electronics hackers like myself, it's cheap, easy to connect to and fun.
I've got a few projects I'm tinkering with for the Netduino and Meridian/P using the .Net Micro Framework, and I'm writing up my experiences over on my IImplement.Net blog, if your interested in the Micro Framwork go have a look.