Read this: http://bjk5.com/post/44698559168/breaking-down-amazons-mega-...

for another useful example of this technique.

This is totally different and makes sense. You simply observe if mouse moves off within a certain angle to not make a submenu disappear. This is cheap and useful. It helps the submenu not disappear when you are moving to it, not having to move the mouse exactly along the tiny space that connects the two menus. This can actually save like 10 seconds each time (inexperienced users)!

The other one will ajax preload a dropdown content when it detects that current mouse trajectory is in line with it. Come on.

No. Similarly Microsoft has done some work to improve input latency by predicting what gesture you're about to do once you start touching the screen.

Given the limited number of gestures this is cheap and easy. This is as easy as "did the user go left or right after touching? Ok, then did it go up or down?".

Analizying a trajectory is a completely different thing.