I have used the service once. ATC was very helpful but then again, the sky was empty and so didn't point out any traffic along the way.
Was flying YPPF - YBLT and faded from radar coverage just on the PF side of Bordertown VOR while cruising at A055 (from memory).
Question for tobzalp - If you don't report changing to CTAF and disappear off radar, will ATC declare a SAR phase. The info. pack that was sent out, from memory, stated that it may trigger a SAR response but ATC would not hold full SAR. Again, working from memory so don't hold me to anything.