Is there any way to activate multisampling with MonoTouch and OpenGL ES 2.0? I can't find the apple extension in the framework, so i think it's not implemented?
Functions like glRenderbufferStorageMultisampleAPPLE and glResolveMultisampleFramebufferAPPLE are not presently included in MonoTouch's OpenGL bindings. I'm not sure if they are included in the latest OpenTK bits.
Anyway whenever you find missing pieces you should fill a bug report (enhancement) on http://bugzilla.xamarin.com That will ensure you get notified on the progress of the bug/enhancement request.
UPDATE: MonoTouch 5.2.3 (stable) has been released and includes OpenTK 1.0 (which defines the mentioned symbols).