Accuracy is spec'd at 3 meters. Most of the reviews were done with SA2005 and 2006. SA2008 is much better, and in the right laptop, has voice alerts. For driving trips in strange areas it is quite adequate and fun. To really be most effective, it needs a co-pilot to run it while the driver drives.
If you want a totally portable unit, the PN-20 is a very capable handheld device that uses DeLormes superior maps. They are the best in that department.
If you want a more global device, then look seriously at the Garmin Etrex Vista HCX. It is capable of worldwide GPS on and off road.