FWIW, I'd also say ride Nadal for Barca and most of Rome, but maybe not all. Obviously as you are going match for match, you can weigh up each encounter. It's not that I think anyone has a hope in hell of beating Nadal at any stage, but if he does start to visibly fatigue, then it may well be best to hold fire from the closing stages of Rome until the French Open starts.
Like BG says, I doubt Nadal will end up playing Hamburg, if he does I'd avoid Hamburg. Again, not because I think he'll get beat (especially early), but it's not worth the risk.
Nadal is as nailed on for the French Open this year as any sporting event you can find in 2008. There is no chance anyone is taking three sets off him.