If you haven't heard the news yet, you must be living under a rock 😉 There is a new CLR in town. Silverlight (fka "WPF/E") 1.1 comes with its own CLR. And the best news is that it runs both on the Mac and the PC.
Go check it out at silverlight.net.
One of the greatest achievements is that the download is a mere 4 MB. If you have a reasonably fast Internet connection you can download and install it in under a minute. Try that with .NET 3.0! That will take at least an order of magnitude longer to install.
This is what the Silverlight directory looks like after the install:
It shows you this CLR is completely separate from the standard CLR 2.0 runtime and has no dependency on it. This CLR has 2.1.x.x as version number. It has no Global Assembly Cache (GAC). You can see that support for dynamic languages like Python and JScript is included. Support for Ruby is in the works.
Go listen to the Channel 9 interview with Scott Guthrie if you want to know how Microsoft succeeded in trimming down the CLR 2.0 and the Base Class Libraries to this size.
The Silverlight .NET assemblies have the same format as standard .NET assemblies, so you can view them using Reflector. The type system is the same, so Silverlight supports generics. It will also support C# 3.0, VB 9.0 and LINQ.
These are exciting times for the .NET world. The reach of .NET has been substantially increased. Not just because the few percent of Mac users can run .NET applications now, but because it is such an easy deployment for Firefox users on the PC. And soon for Opera users as well.