I think I've flagged something....once. Yup. Most everything on the front page is interesting, the most interesting of which I upvote, and the few things that aren't I just don't read and let die. the front page changes enough to allow me to do that anyway.
That's okay; the models are really different. Stack Overflow needs to scale more because to be useful, there need to be thousands of questions asked every day, and every question needs to be able to get a response. Hacker News can be useful to me even if it only gets a hundred new stories a day, and it's not really a problem if many stories get axed for a bad reason.