Slower Pace, I was trying to imply just what you have observed -- there is no practical difference between NAD 83 and WGS 84. NAD 27, however, is different. There can be a considerable difference in coordinate values in this older datum. GPS receivers allow for NAD 27 use as some detailed maps use this datum and no other maps are yet available in NAD 83 or WGS 84.
If you want to explore in more detail issues and descriptions of various datums, both the NGS and NIMA web sites provide access to various documents.
WWW.NGS.NOAA.GOV and WWW.NIMA.MIL
The NIMA site has tr80-003 "Geodesy for the Layman" which helped me a lot.