I'm glad Inertia mentioned this:
But there is also a big decision coming with GL3. Forward compatible contexts.
The way I understood the manual, a forward compatible context will generate invalid-operation errors whenever you call e.g. glVertex3f(). The solutions I see for this are
a) Use compiler conditionals to compile OpenTK either against GL 2.1 or GL 3.0
b) Don't do anything at all. Let the user sort out what's allowed in GL3+ contexts.
c) completely remove legacy extensions and functions. Set GL3.0 as standard.
The discussion definitely needs it's own thread. From my point of view (1/3 way to alpha, mid-sized project) I would very much prefer number three. It will probably break almost all of my code but I'd rather fix a bunch of syntax errors than a single runtime one.