Well i am pretty new with this too but i love MEDIA ENGINE so far.
*external apps is to add icons to say internet explorer or MS word or something.
*GPS, ive read it does have GPS now that i am trying to figure out to, i just got iguidance this week though so well see.
*You can DL the skin editor and change buttons fairly easy and point them to differnt EXE's. An eject button, well that im not sure of but it would make sense.