You know it's hard to count Shields out, he always finds a way to win, but honestly I don't think he's ever fought someone will the type of tools that GSP has. I think GSP avoids the takedown and keeps this one standing much like he did with Koz, but hopefully no broken orbital bones.
As far as Machida and Couture go, it could go either way. If Couture gets a hold him against the cage and dirty boxes him for 3 rounds he will win a decision. On the other hand Couture's chin isn't the greatest and it will only take one punch from Machida. I think Machida fights like his career is on the line and wins via TKO, regardless it's Couture's last fight.