If Valuev was really hurt by Nobles he would not have been able to take that second flush punch. Valuev has been knocked off balance, but I don't think he has actually ever been hurt.
If Haye boxes as open and WITHIN RANGE against Valuev as he did against Gurov then that's the biggest mistake he can make. The entire key against Valuev is staying out of range and countering with very high precision, as Chagaev has shown. Haye has never been able to display any skills to manage range and distance very well, I am curious if that will improve against Valuev. IMO it has to!
Yeah as good a punch as that left hook was I think the stumble had as much to do with him being a little off balance when he got hit as anything else. Watching again it kind of looks like he was just about to step back and set his feet properly when he got hit. By the time the right hand connected he was back on balance and so not only walked straight through it but fired back with a punch or two of his own. Kind of difficult to find any examples of Valuev getting hit really cleanly though, think this and the Bidenko video are the most obvious ones I've seen. Guy can take a punch that's for sure...