As far as Reddit's rankings:

- you need over 10 karma (not comment karma) in any given subreddit in order to bypass the spam filter in that subreddit. Having, say 55,000 karma in all other subreddits does not matter. Comment karma within that subreddit does not matter.

- Having -10 or less comment karma in any given subreddit will trip the comment timer in that subreddit. It is a point of pride of mine that I have managed to trip the troll filter in both /r/2xchromosomes and /r/mensrights because they're both full of extremist morons.

- If there are two comments posted at roughly the same time (think it's within a minute), the commenter with the higher comment karma will have their post appear on top and the lower comment karma will appear below. Note that as soon as their vote totals are no longer equal, the individual comment karma of the poster becomes irrelevant.

That's it. That's all karma is used for on Reddit. That is the sum total of the utility of scorekeeping.

FUN FACT: backintheday it was routine to see trolls with negative comment karma. As Reddit has grown larger, it hs become virtually impossible to amass negative comment karma, in no small part because while Reddit counts the impact of "downvote brigades" on any given page (where it really shouldn't be counted), the voting impact of "downvote brigades" has no impact on an individual's overall score (where it really should be). In other words, they have it exactly backwards: campaigns to silence dissent are chillingly effective but any overall impact on the prestige of any given user is nill.