I tend to either not fav because I can't think of something to say, or get annoyed at the wording and not fav at all, but normally it's the first one. I personally always try to leave a comment when I fav... If I have one fav by the artist I tend to 'fav' a lot less, and just save the picture and move on. XD;
Depends. If I can add something to the comments that hasn't been said, then yeah, possibly, but if i have no time or there's nothing else to say that hasn't been said by about 20 other people already then, no i don't.
Sometimes i get those people who will hunt me down and yell at me for not commenting before i faved. My response is always, "Fine, then i guess you don't want the fave." and i end up removing it.
I understand some people want advice or critique and will say so, and those people I'll always try to leave something helpful, but i hate it when people are begging for comments for the sake of getting mindless praise.
"Sometimes i get those people who will hunt me down and yell at me for not commenting before i faved"
I got lucky, I think that's only happened to me once in the time I've been here
I did come across an art I wanted to fave once where someone had put "Please donate points if you fave", but since I don't do points I commented and told them why I was declining the fave. The response? "Oh you can fave, you just can't use it." Well, the fact that I can't ever see a time when I'd want to use it aside, I directed them back to their own Artist Description XD
I see a lot of these "Please comment if you fave" things. Personally, if I like the artwork I will try to think of a comment, but I hate leaving half-assed comments, and a lot of the time I simply don't have the time to sit around writing meaningful comments for every deviation that I fave (I get a looooooot of deviations in my message center), so generally if I come across that and I can't think of a good comment within a minute or so, I leave it.
On the flip side, if someone faves and runs on my art, and in their user page, or on their deviations they have that written, I will pull them up on it. After all, I may not ask people to comment if they fave my work, but if you ask that of other deviants the least you could do is comment on every piece of work you fave.