I just joined a few days ago and after lurking about for awhile I've noticed a lot of interesting discussions that are 30 days some even 100 days old. I was wondering if posting comments to them is "acceptable behavior" or if I should stick to newer posts. I tried searching for an answer, but I'm not even sure necro-posting is the right term for it.
Yes. Please comment on old posts! It actually re-injects them in to feed to further encourage discussion on old posts. I'm the first to admit it feels weird, but people will see it. Hubski places less emphasis on time. Due to an overwhelming number of requests, there is the ability to add "feed times" is in your settings. I recommend keeping it off though and moving away from the feeling that old posts are irrelevant. I feature 2 or 3 old posts in the Hubski Newsletter. My favorite was this post regarding bitcoin. Ouch.