Hi, my interest in GIS, like many here, is archaeological. I'm an archaeological geophysicist in my spare time and I have written some free, but not open source (yet), geophysics software called Snuffler.
I'm using GIS in my project to map the Roman road network in East Sussex. I mainly use Google Earth, rather than proper GIS at the moment, as I am using a Total Station, rather than dGPS to get my co-ordinates. I measure the edge of the field, as well as the survey area, using an arbitrary grid, then overlay on GE by matching up the edge of the field survey with the aerial photo. Once that is in place though, I can get the WGS84 coordinates of the survey area from GE, convert them to OSGB36 and then georeference the image into Quantum GIS. I've got a good few years surveying left to do, fingers crossed for helpful landowners.