I have 2.0 + 3.0 + 3.5... it's required for my work.

If you want to write some tool by .NET, as a developer I'd say YES. And with version 3.5 you could use script-like cool features such as implicit typing and closure.

As an end-user, I'll say ****! It's slow (take 1+ sec to start) and quite a waste of RAM if you count the framework part loaded for file cache in memory.