David Simmons has been banging around the Smalltalk world producing very clever stuff (although he totally lacks any sense of business as far as I can tell - too easily distracted by tasty hacks). Nonetheless, he has done a scripting language called SmallScript that lives on top of .NET as well as on his own VM (which he calls the Agents Objects System AOS).
A couple quotes from him on his .NET implementation experience are:
[link|http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/33895|http://blade.nagaok...y-talk/33895]
[link|http://lists.squeakfoundation.org/pipermail/squeak-dev/2002-February/009189.html|http://lists.squeak.../009189.html]
So its not awful - but its not great either. It *is* better than the jvm.