I don't have a problem with self-upvoting as long as it's legitimate content and not just upvoting spam for payouts. There's a shortage of curators, you're always the first person to see your posts and comments, and if you didn't think it was worthwhile you wouldn't have posted it in the first place.
I generally don't upvote my own comments because a lot of other people don't seem to agree with that position and I don't want to distract them from the points I'm trying to make by arguing about voting.
For me its kind of tricky to upvote yourself. You are always biased towards your own opinion. On the other hand an opinion is biased anyway therefore it's an opinion :)
Upvoting whatever can indeed be classified as steem farming (or something:)) and should not be allowed...