This is a very interesting fight because on the feet, although Nogueira's boxing is good... I personally have never though his defense was any good (and that's not just from the Mir fight either). Couture on the other hand has alright boxing skills but very underrated striking defense. They both don't kick very often though.
On the ground, everyone knows Nog's ground game and submission ability. However, Couture has a great top game and really good submission defense now. People shouldn't forget that Jacare wasn't even close to a sub against Couture. I know they had a huge weight difference but that was never too much of a problem for Jacare before.
Couture is going to definitely use his clinch game and Nog may not have many answers for that. However, I don't think Nog is going to wear out too much from the clinch.
So I think they basically negate each other strengths and weaknesses. I do expect a lot of hugging against the fence though... more than usual.
This is probably the most exciting fight I can think of atm. It almost overshadows GSP vs Alves.