If you're running a competition where the prize is the SBD payout then a self vote increases the prize pool, so I think that's an acceptable use of self voting. Also if your post is a fundraiser for a cause then self voting could be considered acceptable to help increase the donation. I prefer to add a self vote the following day though, so it allows more curation for other voters

#3 would be a grey area for me too. As a newbie your self vote is hardly going to make an impact anyway, but once you're bigger then the chances are that you don't really need to self vote to reward your post as you'll have a following to do that for you.

I've only self voted a comment once and it was to say something that would be of benefit to the author the more people saw it. My vote was so puny I didn't get it far up the list, but a couple of others helped bump it up some more.

Self voting is like a lot of things. In the right hands it can do good in the wrong hands it's just an enabler of greed, but I don't think it should be gotten rid of just because some use it for selfish reasons.