I have a 26" TN monitor, and I can assure you that you can see differences in the vertical plane. If you are not exactly in the center, you'll notice that the top and bottom have different brightness, and colors fade.
I have a tendency to lean back and put my feet up on the desk, and from below the screen is the absolute worst angle to view a TN monitor.
But, in other news, my Samsung has been ok. You get used to the viewing angle issues and don't notice them as much after a while, until someone posts a thread like this. Since I don't do color critical work, a TN panel is not a real problem for me. It works very nicely for videos, especially if I tilt it down to fit my favorite position while viewing.
Some TN panels are better than others. My older BenQ 24" monitor was regarded as an excellent example of TN displays, and is sharper than this Samsung, but I've grown accustomed to more real estate in front of me.