Mono 1.2.6 is a major update, which introduces a native OS X Windows.Forms driver (without an X server), a Mozilla-based WebControl, basic C# 3.0 support, performance enhancements and many bug fixes. Mono downloads.
This release fixes most OpenTK-affecting bugs, so upgrading is highly encouraged. With Mono 1.2.6 out, OpenTK 0.3.14 is scheduled for release during the next weekend and will contain the new Mono WebControl-based Example Launcher as well as several bug fixes. 0.3.15 will be released soon after, and will include Fullscreen mode support, FSAA and double-precision math. A server move will also take place at some point during the following week (current tentative date is Friday, 21th).
Last, but not least, take a moment and post your results for the the PQ Torus Knots test. This test will detect your video card's vertex cache size, which can be useful for mesh optimization. Thank you!