My personal experiences with Boo were from about 18 months back, and I've not followed it actively since then, so keep that in mind wrt to what I say. It is a cool language. But it is also experimental. What this means in practical terms:
- You can do cool things w/ the language. The macros they allow, plus mixing in good features from ruby and python and other languages.
- There is a WinForms designer you can use via SharpDevelop (which has Boo integrated as a standard development language).
There inconsistencies and bugs at occasionally critical areas because it is not done yet.
I'm not sure if Generics can be created yet w/ Boo, but they certainly can be consumed.
Performance is good, but the compiler doesn't have an optimizer.
Type inference is cool. Duck typing is cool. All that lets you approach the illusion of dynamic typing.
Personally, I worked on a tool to make creative writing easier. Think IDE for writers.