I have an Ipaq, and bought the Tom-Tom 3 from click here
I have used it extensively in the UK and, (with the optional European maps), during my 2500 mile tour of France this summer, and it has proved invaluable. It seems accurate to about 6ft, and if you need to deviate from the route, (e.g. a road closure, it quickly re-calculates a new one).
I found that you very often need to do a soft reset of the Ipaq when setting a new route and plugging in, even with their latest 3.03 download. However, this is only a minor inconvenience. Their mapping seems excellent. There is lots more I could say, but if you need more information, contact me direct by clicking on the envelope next to my name.