I don't think of it as really good or really bad... As with everything, there are two sides to it. And for me personally, I think the advantages are more than the disadvantages. However, I'm still very careful with what I say or do on the internet, and I certainly try not to stay on it to long. I wouldn't want to become like my little brother who'd like to be online for the rest of his life
One of the biggest advantages, however, is that I learned to express myself more on here. It has helped me a great deal in real life as well...
"Good" and "bad" are moral concepts, which qualify actions, not things. The Internet isn't good or bad, it can be used for the good and for the bad, just like cars, hammers, nuclear physics or baseball bats.
All in all, though, I think the good uses of the Internet outweigh tremendously the evil ones. It is definitely one of the greatest achievements of humankind.