As some of you may have noticed, in the initial release of OBDotNet the enumerator types are not mapped correctly. The proxy classes are generated but the parameter typemaps have a problem and no operators are overloaded. As a temporary fix, this gist contains some extension methods for enumerating atoms and bonds.
I threw this together kind of quickly and only did a little testing, so please email me if you see any bugs.
To demonstrate using these enumerators, here is a simple C# version of Noel's python script that calculated a circular fingerprint using the OBMolAtomBFSIter
Addendum: If your application is targeting v2.0 of the framework this MSDN article contains instructions on how to add support for extension methods. The relevant section is about 90% of the way down under the heading:
Extension Methods in .NET Framework 2.0 Apps