I just purchased two new computer monitors, one for the office and one for home. Maria at Teaching College Math said she didn't know how anyone could live without one. After considering it, and shopping for a deal, I took the plunge. So far, no regrets.
A second monitor lets you have expanded desktop viewing of your computer on two different monitors. You can have your internet browser open on one and a Word document open on another while controlling both with one mouse. If you invest in a little real estate, you could easily see multiple documents on one or both of your monitors. It eliminates the need to switch back and fourth between applications. You can work on a PowerPoint presentation while keeping an eye on your Camtasia project or those eBay bids. I wouldn't have blogged about this but I ran across this research article that says having two screens or even three can improve productivity by 9 to 50%. I believe that I can see a difference already. I usually have so many applications open that I'm sure that I waste an hour everyday trying to find the one that I want to switch to. Having room to lay them all out helps.
Connecting to my laptop was foolproof. But I am having problems getting connected at work. Not enough places to plug into on the back of the CPU. Until I get it figured out, I just switched my new 20" monitor out with the old one. Wish I had done this a long time ago.