Lanefan
Victoria Rules
I don't see this as poisoning discussion at all, rather - given that in my eyes some of the listed-upthread forms of metagaming take a player well into the "jerk" spectrum - it merely serves to clarify it.When we put being a jerk on the spectrum of metagaming, then we're effectively saying that there's a little bit of that end of the spectrum the bleeds through the rest -- that metagaming is at least associated with being a jerk and cheating and whathaveyou. I find that this poisons discussion.
Some others, however, I don't see as metagaming so much as just playing the game. Knowing you're playing through a module, for instance, or even what module it is, isn't really metagaming; but having and using prior foreknowledge of that module in play (e.g. knowing its secrets via having read, played, or run it before and acting on that knowledge) is metagaming and IMO verges on (or is) cheating.
Oftentimes before running a canned module I'll ask the players if they've hit it before, and if someone has then I'll go to plan B. Other times I'll run something they haven't seen in ages and rely on faulty memory and-or change it up just enough to make a difference.

I'm also pretty hard-line on trying to keep player knowledge and character knowledge the same where-when I can, in full realization that such is not always possible and that sometimes one will know more than the other in either direction.