I've been hellbanned here on HN on at least three different IP addresses and accounts...that I am aware of. Probably more.
In each case nothing I'd ever said would be considered trolling by any rational observer. Here on HN, however, as with most communities where you start to recognize the regulars (tptacek, raganwald, etc), "trolling" is redefined to simply mean "going against the grain".
There was one discussion that I participated where I predicted that Apple would see declining profit margins due to increased competition. Remarkably this completely benign, seemingly obvious observation saw me declared a troll, and shortly thereafter yet another account was hellbanned from HN (whatever the mechanism -- is this the verdict of a bored PG, or has he anointed some particularly under-employed members to apply it? -- it is horribly broken).
Troll is, more often than not, a term used to circle the wagons.