It's been an interesting situation. We might never know the exact impact the RRoD had on the fortunes of the 360. Would it have sold more units without the negative press? Would it have actually sold less units, since so many people have owned multiple versions? I don't know. Not that it really matters, "total units sold" is kind of a fanboy metric; Microsoft would certainly rather have sold fewer units if it meant not taking such a big loss from a financial perspective, not to mention the damage to the brand's reputation. I think a lot of people forget that the bottom line is profitability, not bragging rights.
It's also interesting to wonder what impact it has had on the 360's installed base. I know the PS3 and the 360 are neck-and-neck in that regard, but the last report I read on that subject had the PS3 inching ahead. That obviously shouldn't be the case, given that the 360 has sold millions more units total.
Regardless, Microsoft has to be happy that the RRoD is mostly in the rear view mirror. You don't what that kind of thing to still be in people's minds going into a new generation.
