I used to wish for Dawn's violent death to come every episode when I first watched the show, especially during Season 6. Poor Dawn, lol. But, now that I've watched it a million times with a different, more fun, attitude, I like her a lot more. I think she's fun in the beginning of Season 5 when we're still learning about her character. Not so much in Season 6 when she's being a complete....well, attention starved brat to Buffy (which I can see where she's coming from, but still), but she redeems herself in Season 7, I think.
So, I'm kinda on the fence where Dawn's concerned. I like her and dislike her depending on the season or episode.