I don't think I'd personally replace mapping with a GPS BUT when looking for tricky sites it is great to be able to plug in the grid reference and follow the arrow...

G

ps - for the techies...at work we are testing the use of electronic OS mapping (down to 1:500 scale) loaded on PDAs to map refuse and recycling collection rounds (the cutting edge ;-)). This is then uploaded to our MapInfo GIS system to save the bother of paying a GIS technician to weave his magic. Of course I will test the system at weekends but it only covers my Borough!