I have traveled with a number of GPSs and here are my experiences:

1. Garmin eMap
Pro: Compact to travel with. Use 2 easy to find AA battery. Enough battery life to record a Frankfurt to SFO flight
Con: no auto-routing, memory is limited to 128MB.
2. Garmin Streetpilot 2610/2620/2650/2730
Pros: Very capable in a rental car.
Con: No internal battery. A bit heavy with the DC cable, remote and friction mount. Easy to leave something behind.
3. Garmin Quest (also Quest 2)
Pro: Long internal battery life. Auto-routing is good for driving.
Con: Screen is a little small. Expensive friction mount that seems to be no longer available. Need to carry a charger on a trip.
4. Garmin GPS 10 (also Mobile 10/10x)
Pro: Very compact. Works well with a PC. Map size only depends on SD card size.
Con: Using it on a Treo650 is very hard and crash often. Hard to use with a PC while driving.


Also considered the Garmin Nuvi series but battery life is too short for a long flight.

p.s. Also left the Garmin GPS10 stuck to the top of a Hertz rental car. But they found it (still on the roof) and sent it back to me.

Added:
Item 2 obviously need a C seat to work in a plane. Item 4 needs a working PC or phone to work in a plane. Item 1 and 3 can work discretely and get the whole flight path. I got the rapid climb out of Milan over the Alps and down to Frankfurt recorded on my GPS. Once I was on UA metal, I obeyed the rule and miss the ascend and descend of the flight.

Added more:
The Garmin GPS 10 is compatible with Palm OS and Windows Mobile Smart phones. The Garmin Mobile 10 is compatible with Symbian (Nokia and Sony/Ericsson) , Palm OS and Windows Mobile Smart Phones.