"Jim Davis" schrieb

They're like any other piece of electronic equipment. Either you like
it, or you don't.

True. I must admit that I tend to "don't", in most cases.

I have my own unit, which I carry in my computer case.

Your own unit might indeed be a good solution until the car manu-
facturers agree on a certain standard*)
You know how to use it and can take it from car to car, or have it in
your pocket when you walk through a city (I have no car, and usually
use public transport and my two legs)

It's definitely a time saver when you have a tight schedule.

I know they can be very helpful for many. But when I have a tight
schedule I'm in places where I know my way around.
I only rent a car for holidays or a weekend in the countryside - If I
get lost: So what? I'm never in a rush when I sit in a car.
For *me* GPS is just a fancy gimmick I don't really need, but if
a rental car is equipped with one I want to be able to use it straight
away.

Jochen
*)they managed to do that with light switches, gear positions of
both manual and automatic transmissions, and many other knobs
and buttons in a car, so they will come up with a solution for GPS
and all the rest too - eventually. Never give up hope ;-)