Not to be outdone by sponsored research from Microsoft coming to the conclusion that Microsoft is better/faster/more productive and uses less calories, Apple has recommended that 30" monitors increase worker productivity compared to 17" or 19" monitors. Todd Weiss writes about it here.
You don't think that it's a coincidence that Apple has some 30" displays? No, couldn't be.
As an aside I checked out an Apple 30" display in the local Apple store last weekend. Gads the thing was massive, I felt like I'd have to sit on the other side of the room to not have to move my head looking at it. Still a bit pricey for my pocketbook (unless of course you use Scoble Finances, which involves just putting big expensive things on your credit card... :)