I'm proud to say that I was one of the people who helped introduce the +1 reply to messages here at this site. I initially thought I was the first because I had never seen it before, but it looks like wily mo beat me to it by several months.
That being said, I got the idea for +1/0/-1/ from listserv voting. Someone proposes, let's say, to add a new feature to some open source software. They post it to the mailing list, and people reply with +1/0/-1 in the email. It's a very crude voting system, but it's been around for a long time and is very effective.
I've been seeing some posters replying with +2 or +100 or +100000000. Let's try to not over do it. Each one of us is one person, we would get one vote. If you're REALLY REALLY REALLY in agreement with someone, posting +10000000 just makes people ignore you - try replying with a clear explanation WHY you agree. Back up your stance with substance instead of just showing everyone how totally excited you are that someone has the same viewpoint as yourself. Vote someone +1/0/-1 if you want to use those semantics, otherwise you're defeating the purpose of the whole thing.