Fairly regularly. I'm not extremely active in the way of commenting and writing posts of my own but I love the setup to the site. There's so much content out there that you can really build a feed that will show you nothing but exactly the type of things you are interested in.
I post links mostly to my profile. I have only several comments. I am not very active in subreddits. I could have problems with moderators and trolls. There is a Serbian community on Reddit and because of it, I prefer Reddit over its competitors. Reddit competitors don't allow posting to user profile.
No, I haven't. I've looked it over before and it has a lot of info and interesting sub-Reddits but I've never joined it. Maybe some day.
Occasionally, I have read some Reddit posts, but not often.
No, not as of yet but I do know several users on Reddit who keep me informed on interesting information. Perhaps, one day, I will join but not today.