Autosteer is quickly gaining in popularity. From looking at the farm equipment in my area, I'd guess that 40% have GPS systems on their tractors/combines based on observing the antennas on the equipment. Precision farming is becoming important to increasing yields and reducing costs.

Right now, Kinze are heavily touting their autonomous system for grain carts: http://www.youtube.com/watch?v=MhA5aIw7xNk

John Deere and CNH have similar systems in actual production, but still require an operator to be present for safety reasons. And safety seems to be the big limiting factor. While the technology is basically there, nobody wants to remove the operator just yet. Though in this video, someone disabled the safety sensors to go fully autonomous: http://www.youtube.com/watch?v=zU4liQvrcm4

Most farmers are pulling their RTK data over wireless/mobile internet connections, rather than having their own base station. I don't know of anyone who maintains their own station. A few companies have placed base stations around various places in the countryside and will happily sell you their data.

maybe interesting:

In Europe (and of course in Germany) the federal governments offer realtime gps correction data via IP or 3G (radio was shut down a few years ago).

They offer a precision of 1cm-2cm used together with GPS/GLONASS

PDF: http://www.sapos.de/pdf/Flyer/2004Flyer_e.pdf

(Sorry, German language only:)

http://www.sapos.de/ http://sapos.bayern.de/service.php