On one hand, I met the famous Jay Anderson of Rice last week and he's a very nice guy who ended up helping me out a lot. In that case, collaborators are good because you can use other people's knowledge instead of inventing the wheel yourself.
But there are seagull collaborators too, they fly in, squawk a lot, shit on everything, and then leave. If you keep score, it's really surprising how many good collaborators a seagull one can negate.
There's one Italian guy in my group who sent me a two page email this morning. On the negative side, he called a bunch of things that I did "a nonsense" but then logically said what he thought should be done instead. The end result was extremely positive.