Prevalence/importance of online collusion

[luckycharms]

I play a bit of online poker, but I don't seem to do as well online as I do in live games. I'm not gonna moan and groan about it, but it (as well as all of these "collusion" posts) make me wonder how prevalent and destructive online collusion is.

How often do you think it happens at any one table?
With 2 people or more?
Is it really all that destructive?
What can colluders do to win more money off me?
Would they even care to do it in the lower limits?
What can I do to counter it?

Thanks a million