I assume we're talking here about AAs/AAAs, not the high power fronts with their own big battery pack?
Apart from that, I have used rechargeables temporarily, but mostly it's ordinary one-time alkalines.
If I switched to rechargeables I'd have to make sure of always carrying spares. I'm worried about the 'suddenly dying' syndrome. And with the rear, on a busy road, it's not easy to be constantly checking that it's OK (try waving a hand behind your backside...)
While we're on the topic, what's the input on battery 'memory' (Ni-Cd's especially)? True or false? And is it a problem only on Ni-Cd, not on Ni-MH or Li batteries? Because this affects whether you should re-charge early or wait for the battery to die.