In reply to jon:
We did this route about 2 years ago. We bivvied and left bivvy gear about 2 miles up from the road which just left a very short walk to the foot of the climb. Despite the weather becomming pretty fetid as the day went on the reached the summit after about 12 hours, sat around feeling knackered for a while then jogged down past the seracs (the most exposed part of the whole day!) in the fading light to arrive at the Refuge des Ecrins shortly after dark. Collecting the bivvy gear with nothing else to carry was easy the next morning.
The rock was quite loose in places and where it was worst we found some of the climbing to be much harder than the grade would suggest and with none of the in-situ tat you might expect on such a classic route. I think this says more about our route-finding than anything else but do be careful, it is a long and loose enough without extra detours.
Incidentally, in the hut, look at the times on the wall for various record running up the Barre des Ecrins - completely bonkers.
Best of luck