I have a difficult time making conversation with people face to face. I don’t know why, but I do. If I’m at a party or some other social gathering, and people start talking to me, it’s a real struggle for me to find things to say, particularly if I don’t know the person actually doing the talking. Online, specifically on Twitter, I’m far more eloquent with people than I am in person. There’s something comforting in knowing the other person can’t see your face and you can’t see theirs. You don’t have to worry about them judging what you look like or what you sound like, because all they have to go on is the written word. I also tend to believe people are more honest online than they are in person, again, because you don’t have to worry about being judged. They don’t know you, you don’t know them. The other side of the coin is that the same anonymity makes it a lot easier to lie as well, but unless you’re a sociopath or a pathological liar, you’re going to be honest with people more often than not.
As for communicating emotion and intent, I suppose a lot of that is down to how well you know the person you’re talking to. I know my friends’ sense of humor, I know how they think about a lot of things, so I don’t spend a lot of time guessing what they meant by something — I already know. Emoticons or emojis come in handy for this a lot of the time, because a well placed winking face ( ;-D ) can clarify that what you’re saying is meant to be taken humorously rather than seriously. Without resorting to making faces out of punctuation, you could always specify that what you’re saying is only in your opinion or something to that effect, if you’re really worried about what you’re saying possibly being taken out of context.
Of course, the ultimate remedy for that is, if you’re worried someone might take it the wrong way, just don’t say it.