There is no "or." The answer is "yes." The internet doesn't improve your verbal communication, but it most certainly enhances your ability to communicate, though not always in the ways you imagine.
Look at Twitter feeds, so-called "txt-speak," and those two-sentence memes that are always being passed around. They often look garbled or are simplistic to the point of hilarity, but what's actually happening is that people have learned to boil down what they want to say into a very, very small space. They're getting down to the nitty-gritty of language, the absolute root kernels of communication, and are managing to say quite a bit with very little. There are all kinds of shorthand tricks to get extremely complicated things expressed via text ("/s" or "kappa" letting you know they're being sarcastic, for example).
Sure, if you look at these things from the perspective of a Grammar Nazi like myself, it looks like madness and anarchy, but it's completely the opposite--it's an extremely efficient system cobbled together through trial and error by people dedicated to making language simpler and more transparent. Even if it looks like linguistic heresy.