Do multiple monitors actually increase efficiency?

Not on account of making it easier to multitask, I think. But I had an internship where I spent a decent amount of time taking comments and revisions from Design Review and making the changes in AutoCAD, for which two screens would have been a huge time saver. It's much more time consuming to do that sort of editing when you can't see the comments and the drawing you're working on at the same time.

It was a small office, and the workstation I was on was only used when they had an intern, so it wouldn't have been a high priority. But you can get a 17" screen for $100, and I'd bet I would have had at least $100 more productivity on drawing revisions if I'd had one.

Multiple monitors don't even have be a major productivity booster to be worthwhile. If an employee's annual cost (salary, benefits, other expenses) is $100,000, an extra monitor is a measly 0.15% more. If that one time expense makes the employee 0.15% more productive the monitor pays for itself multiple times over its lifetime.

If your a coder is sure as hell does. I couldn't live without my two 22"s. Code on the left, browser on the right.

...I could maybe even do with another ;)