I had not heard of Mortplayer, I'll have to check it out, though I don't have an Android device to be able to get a good look at it.
You are correct in that the app places the bookmark for you. It basically remembers where you were in each file.
How do you use the "tag different places in a file" type feature in your audiobook listening? I generally am just listening to novels, and don't have any real need to jump to various spots in the same file.
The reason I ask is that I'd like to implement features users would use, but don't want to overly complicate it with feature bloat.
As an update, I have implemented and am testing three new features. Once I make sure it is working as expected, I'll submit the update to the marketplace:
1) Configurable port on the loader (8001 might not be convenient for everyone. Should have thought of this before)
2) Run under locked screen. Now you can lock the screen to save battery power
3) Configureable sleep timer (with optional shake to reset).
I hope to submit it in the next day or so...