Via Engadget (and Smart Mobs) we have news on a location-based tourist application for Amsterdam, from TimeSpots, which you can rent at major hotels for a fixed daily fee.
Cool! I would go for that. When we where in Spain last year (fall 2003), I was jotting down brainfarts on a similar GPS guide concept to help with a) Navigating the unfamiliar streets (i.e. where am I and how to I get to X) b) Tell me about X (i.e. this building/place and it's history, what did it look like when X happen or 100 years ago).