One advantage the Arduino has over the Netduino is a lot of high power GPIO lines, 13 of them each capable of 40mA which poweres 2 LEDs per IO line fairly brightly, and 6 of these can be run as PWM which make LED's appear go dim or bright.
Armed with a spare Arduino, a little too much time on my hands, a ghost that needed adapting from 110V to work in the UK and a bunch of white LEDs I set about making an Arduino powered Ghost ready for Halloween.
Here's the result (first 12 seconds are dull, hold on in there):
Warning: This video contains some images of bright flashing LEDs, don't watch if you are affected by that!
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.