There's a habit within Canonical on expressing agreement and disagreement numerically. If we agree with something someone says in email or IRC, we'll often say "+1", which means "I agree!" or "if we were to vote about this, you would have my vote". I sometimes hear people actually say the words "plus one" in conversation.
Some have extrapolated from this to say "-1" to mean "I disagree", which is a pretty natural thing to do. However, it confuses me a lot.
You see, the "+1" thing is a little bit like the Apache voting system, which I met in my early days of open source, back when I lurked on the Subversion development mailing list. The voting rules there were burned into my mind, and I foolishly assume that they are equally fundamental to everyone else.
In the Apache system, "-1" means "veto", which is a very strong way of disagreeing. When people on the Launchpad say "-1", I never really know what they mean. I don't blame them, "-1" is a bit of a silly way of vetoing a proposal. I bet if keyboards had a key for ∞, there'd be a much more sensible way.
I guess the moral of the story is, "ambiguous shorthand is ambiguous".
Incidentally, how does the Apache voting system work out in practice these days?