Mono 2.4.3 was released yesterday. It's largely a bug fix release. Here are the highlights from their release notes relevant to OpenTK development.
Upgraded xbuild, our msbuild implementation, it should compile more projects.
Fine tuned memory usage, improved performance in various server loads. This release also contains many updates to the Mono Debugger, Windows.Forms, ASP.NET and ADO.NET.
The debugger works on OSX (but you still need to run it as root on newer OSX releases, or build the Info.plist into your program).
I'm looking forward to trying the debugger.
Edit: Well, never mind on the debugger, apparently that is an error in the release notes.