Regarding this GPS conversation, I think I should have payed more attention in school, as you are making my head spin. Haven't got ANY idea what you're talking about, but sounds interesting :-)
In a nutshell WAAS is a free service covering North America which gives you a correction for the errors inherent in the GPS system. It gives you accuracy within 10 feet normally. More and more cheap consumer receivers support it. While some third-party sites say the Nikon GPS-1 supports the WAAS satellites, Nikon's website doesn't and their accuracy claims are more inline with an autonomous position. Since Nikon likely isn't designing their own GPS chips this feature will likely come to them for free if/when they release a GPS-2 - most of the newer chipsets on the market today support it natively.
Differential GPS is the style of solution correction which is at the heart of WAAS. You can use WAAS, one of a number of subscription services offering coverage outside north America, or higher quality within North America. You can also run your own correction station. Cost is from $100/yr to $20,000 in equipment. This is truly a specialist solution. I'll wear a dress and call myself Nancy if any of the camera manufactures ever offer a (non cellular and non WAAS) differential service.
Kinematic GPS is another style of solution correction. It must have a base station within 10km of the rover (ok, some exceptions apply), and can give you sub-cm accuracy. While it is completely overkill if the desire is sub meter vertical it is the only way to be sure - as kinematic (unlike differential) involves a robust initialization which is constantly verified.
http://en.wikipedia.org/wiki/Real_Time_Kinematic (not the only way to do kinematic, but the only way discussed in depth on wikipedia.).
AT LEAST $10,000 in equipment cost.
This too is a very specialized setup and will likely remain so for a long time to come. Farmers are just now starting to use it but their needs for precision location is far from us photographers.
Or you can post-process GPS data recorded with a dual-frequency receiver ($1000 minimum) and get great solutions. There are two main ways to do this. One is static GPS which (as the name implies) is only effective for a non-moving receiver but can give you insanely tight results, the others are post process versions of the differential and kinematic styles mentioned above, with the quality being as mentioned above as well.