I'm not actually sure if it's been used for real, and I don't think it's really been needed - apparently it's rare for GPS ephemeris data uploads to be late by even an hour or two. In principle the idea is that it would be operating all the time and give slight accuracy and integrity monitoring improvements, but that doesn't seem to be a priority.

Incidentally, it seems like the EU is looking at developing their own version of Autonav for the next generation of Galileo, quite possibly with optical rather than radio links between the satellites.