It's very easy for people to project a particular persona when they are on the Internet. Build yourself an identity, hang it on a frame of some carefully crafted photos, and you've fooled some people. This has happened to me at least twice so now I'm always a little careful.
Because of this I always tell people that their view of someone might be skewed until they meet in person. You might think someone is a certain way but you made a subjective assumption based on your limited means of interaction with them.
Imagine my surprise and delight when I met 8 members of my World of Warcraft guild in Las Vegas only to find they were, if anything, nicer than what I had assumed - and I already thought they were really nice. We had a long weekend of chatting and socialising, it was absolutely brilliant. Just goes to show that while you are probably right to assume that most people on the Internet will harvest your organs sooner'n look at you, it's good to be pleasantly surprised now and again!