I'm getting these weekly updates from Yahoo that shows comments from people I have on ignore, so I'll try to make it easy to understand how I at least decide who to ignore:
1-If you are posting one of your first posts on record under a given id (which Yahoo makes it easy to check), and you can't even make the effort in a title to spell a key word correctly, you are showing little to know desire to seem credible on the most basic level. So you are put on ignore.
2-If in looking at the history of a poster's comments, the majority of those comments are either not the appropriate subject for the board, are crude, or political or all some combination of the these traits, you are put on ignore.
3- If you are clearly a paid basher or spammer. It is not worth describing ALL the examples, but one typical one includes titles that are promising one thing and then listing a site to a spam site of some kind, you are put on ignore (if it doesn't take too much of my time).
4-If you continually bait and switch with your comments and make boastful claims about what the charts say will happen today tomorrow or whenever and 'promise' this thing is doomed to crash to this set price, etc, you are put on ignore. (I actually do this for silly claims in the other direction too but that really doesn't come up nearly as much.)
I think there may be a couple of other less common traits in a poster, but these are the main ones for me. So, I'm fine with posters that actually say something constructive (and critical) of the stock but that rarely happens because most of those negative posts show little thought and effort and are usually very transparent in their intentions as a paid basher.