Generally, they are a little thinner from top to bottom - however getting a higher resolution bigger screen (22" 1920x1200) more than makes up for this!
I have two monitors and really want a third - The fact is, one is not enough for modern day work, two is a good amount to work with as it allows you to compare / reference whilst working but I think that three is the best amount as it means you can do your dual monitor work whilst having a third for your every day stuff (internet browsing, refreshing superuser.com! etc.)
I have seen many people with widescreen monitors that use them for displaying two windows side by side, however I really just can't work like that... Another good use that I set up for one customer is to rotate them and use them portrait. (My client has three with the middle one set up like this - it is amazing!)
Anyway, go for it - you won't regret it. Just make sure you get at least 1920x1200, DVI and HDMI with HDCP and it should last you for years to come!