The audiobooks on the ipod are tagged as such. This means they have a bookmark feature as well as speed settings etc.
If you import your own audiobook CD's they will not be recognised as itunes audio books, just as a normal CD. However you can convert them to being audiobooks with all the advantages of them.
Click here for instructions
I think there is a simpler way with applescripts but it escapes my monday morning brain for now.
Of course, this is an iTunes thing, and will not apply to fake ipods etc etc etc.