I've finally given in, and implemented a '2d-cursor' for the Graph Editor. This is simply represented as an additional horizontal line that meets with the current frame indicator, forming a cross-hair. It can be disabled from the View menu. Currently, the only tool which takes this into account is the Snapping tools (Shift-S), where I've hooked up a tool I added some time ago. TODO: - expose this cursor to the transform tools for scaling/rotation options...