Looks like someone is building a Smalltalk implementation native to .NET - have a look at the Vista Smalltalk blog. This is a great explanation of the value, to my mind:

As internet connectivity improves, we will increasingly be building ad-hoc, highly connected applications. Think of how online games or workgroups might evolve as Peer-to-Peer networking becomes commonplace, or think of how applications aggregating data simultaneously from dozens of webservices might evolve.

We will need a more powerful way of doing programming to build ”instant” applications robustly and quickly.

Smalltalk originated in the powerful biological concept of “protected universal cells interacting only through messages that could mimic any desired behavior (Alan Kay)”.

With its simple messaging paradigm and minimal syntax, Smalltalk is probably the best language yet invented for harnessing the increasing potential of the Internet.