You are limited to 1080 vertical if you get a 1920x1080 widescreen.
You have more choices with 1920x1200. You can use all 1200 vertical pixels if you want, or you can drive the monitor at 1920x1080 (with letterboxing at top and bottom). So you have the best of both worlds if you go 1920x1200. But that's one of the reasons why 1920x1200 monitors are more expensive.
I'm running a 1920x1200 display, but when I play Starcraft 2, I use only 1920x1080 to display more of the battlefield. I don't even notice the letterboxing strips on the top and bottom (60 pixels tall each), your brain adjusts to ignore them. Also, you get a FPS boost because you are driving less 3D pixels. The reason SC2 displays more info in 1920x1080 (16:9) is because they "crop" the left and right sides off ("zoom in") when you drop down to 16:10 or 4:3, so you miss that part of the screen if you aren't running 16:9. Not all games do this - some FPS will enable you to see more of the top and bottom view by running 16:10 or 4:3, compared to 16:9.
It's a sad truth that most websites don't take advantage of widescreens (for example, the AnandTech Forums where I'm typing this message - lots of white space to the left and right of my text entry box for composing this post). You can compensate by running two browsers side-by-side, but that setup looks better on 1920x1200 than it does on 1920x1080 anyway, because 1920x1200 gives you more vertical space - and that's where the information is arranged for websites, in the vertical directions.
If you do any work, 1920x1200 is much easier to view 2-page full-spread facing pages (8.5x11" pages) because you have more vertical space to maximize the 2-page spread.