In reply to IainMunro:
It's not as long as 150m I think... more like 100m or less. I crossed it back in early September on the way down and it was fine, just walk quickly across after looking (and listening) for any debris coming.
However:
Why on earth do you want to go this route? The three summits is a FAR more enjoyable way to do M Blanc. In September I went up the 3 summits, and we decided to go down via Gouter for some variety. OK so the ridge down from the summit is quite nice, but as soon as you get near the Gouter hut (which truly deserves to be demolished - you can smell it about 500m away) the fun ends. Going up this route with all the tourists after staying in this stinking hell-hole is NOT my idea of a fun day out.
Climbing down the Gouter ridge isn't much fun either, it's just a great heap of rock and crap, and there are plenty of slow people bumbling about on it knocking stuff off.
Once you come down the ridge you've got the Couloir to deal with, which was a bit of an anti-climax after hearing everyone say how dangerous it was.
After that you've got a long boring walk to get home, especially if the train isn't running like the day I went. Fortunately my climbing partner generously broke his ankle in a bizarre accident and we took a helicopter down to Chamonix!
Tim