This becomes a fascinating question when one considers two or more racing bikes (e.g., RR and TT), two or more wheel sets (e.g., training, race and disc) and backup strategies. While I haven't made my final decisions, this is how I am leaning at the moment.
Power Meter: PT SL
Training Wheels: Campy Montreals, two rear wheels, one w/ PT Pro hub
Race Wheels: HED 3 Carbon (front & rear) w/ PT SL hub on rear
Disc: HED Disc w/ PT SL hub
If my HED 3 hub goes on the blink, I will race with my training wheel. If my HED Disc hub goes on the blink, I will race with my HED 3 Carbon. If my training wheel hub goes on the blink, I will train with my backup non-PT hub. The entire power meter setup (2 computers and receivers, 2 SL hubs and 1 Pro hub) is less than the cost of one SRM Pro.
I should also note that you won't find the HED 3s or HED Disc on sale anywhere with a PT hub.