I flag articles that I don't think are up to HN standards. I seem to recall there was a discussion that said that was an acceptable use of flagging: in any case, that's how I've always used it, as a sort of "I don't think this should be here" button.

This article in particular, because it was sensational rather than debate-worthy. "This is why I wouldn't buy a Kindle" versus "I wouldn't touch the filthy, rotten awful thing even if you gave it to me for totally free." I thought it was worth a flag.