Just downloaded Pocket Streets into my Smartphone. Surprisingly useful. A big chunk of the North of England came in at around 9 Megabytes of memory. I wish I'd managed to get this to work before we went to London. The view is of course very small, but the fact that you can search it and find places is very useful. The zoom is a bit slow (perhaps this is because I've put such a big chunk of england in it) but overall very useable.
I've also been playing with MapPoint and my GPS device. Works OK in terms of telling you where you are, but it is not a portable navigation system as such. However, if you add Advanced GPS, which you can find
here, it may be. For a mere 10 dollars this seems to add direction giving abilities to MapPoint, as well as allowing you to set the baud rate for your GPS device (something which the very stupid MapPoint program will not let you do). I've not used it in anger yet, but if it does what the web page says it does it could be very useful.