I used the formulas in Designing Great Beers by Ray Daniels to calculate the hops.
The tricky part is the difference in utilization on a commercial system vs. Homebrew systems.
It seems like there are so many more variables to consider in hop utilization. I think mash efficiency works out more consistently because the results seem to "bend" toward a specific point, the "knobs" we can use to control it are fairly well understood, and the results are more easily measured.
Most agree that all IBU's are not equal, but even if they were most people don't measure IBU's on every batch (or maybe any). So we're left to taste the beer and then try and reverse engineer what changed the hop profile. Was this batch of hops fresher, was my pH a little bit higher, did my wort stand above 180 a few minutes longer than usual?
I heard an interview with Glenn Tinseth once (I think on Brew Strong). It was a great reminder that there's so much more to learn on this front, and that what is already known is still pretty rough and impacted by a lot of variables that are not well understood.