Apple hired a company to study the productivity impact of using a 30 inch monitor as compared to a 20 inch and 17 inch monitor. The results indicate that a user on a 30 inch monitor will save about 1.3 hours per week over a user on a 17 inch monitor. The report is based on what they consider to be normal usage.
This isn’t a huge productivity gain, but it might make it a little easier to justify upgrading your monitor. Also, even small productivity gains add up. At 1.3 hours per week, you’ll be getting over half a day of savings each month.
Depending on your work, the savings in productivity could be much greater. If you work with many different applications at the same time while moving data between spreadsheets, word-processing documents, and websites, you could potentially see an even bigger return.
The report is in pdf format and can be read here. Obviously Apple isn’t impartial. They want a positive report in order to increase sales. There is good logic behind the study, but it may not take into account some of the downsides of having an extra large monitor–for example, you might find yourself unable to resist watching movies on it when you should be working.