mouseEntered: and mouseExited: don't track entering/exiting your view directly; they track entering/exiting any tracking areas you've established in your view. The relevant methods are -addTrackingRect:owner:userData:assumeInside: and -removeTrackingRect:. Just pass [self bounds] for the first parameter if you want your whole view to be tracked. If your app is 10.5+ only, you should probably use NSTrackingArea instead as it directly supports getting mouse-moved events only inside the tracking area.
Keep in mind that 1) tracking rects have the same somewhat odd behavior as cursor rects w/r/t rotated views, and 2) if your bounds change (not merely your frame) you'll probably need to re-establish your tracking rect, so save the tracking rect's tag to remove it later.