For quite a few versions now, the project is compiled with the C# 3.0 compiler, while still targeting the framework 2.0. I don't think there was any part of the code that actually used C# 3.0 features though. It's always a bit hard to know which features are pure syntactic sugar that will compile directly or if assemblies from the framework 3.5 will be needed.
I have just added LINQBridge <http://code.google.com/p/linqbridge/> as a dependency (BSD licence). It's only in sandbox code but will be comitted shortly.
This small assembly (60KB) basically allows us to use the features of C# 3.0, like extensions methods, the Action<> and Func<> delegates signature, LINQ queries, ? expressions, etc. (still targeting .NET 2.0)
It just struck me as odd that Kinovea was a pet project to experiment new stuff and technologies, and that it was stuck in a 2005 language ! (The move to Mercurial DVCS follows the same logic)
joan. PS: I'm using both SharpDevelop 4.0 and VC# Express 2008 as IDE.