Mine's almost entirely M4A (MPEG 4 I believe), with some MP3 which were ripped from CD before I had iTunes.
The USB stick is NTFS.
Ours isn't random, in terms of "not going back to where it was when the car was turned off".
It has two memories.
If the car starts up with Memory 1, then it DOES remember what it was doing under Memory 1 when you turn the car off.
If the car starts up with Memory 2, then it DOES remember what it was doing under Memory 2 when you turn the car off.
What USED to be random when we first got the car was whether it would start under Memory 1 or Memory 2. Now that my wife has been driving the car 9 times out of 10 for the last 2.5yrs, when she uses her key-fob the car always starts in Memory 1. When I use my key-fob, the car starts in Memory 1 maybe 75% of the time, and in Memory 2 ~25% of the time.
Note that these memories aren't only the current track off the USB stick; if the car starts under Memory 2 and something's playing off the USB stick & then I change to FM, then the FM station is stored under Memory 2. So the next time the car starts under Memory 2, it goes to FM and the specific station which it was tuned to.