Two problems with this approach:

1) if someone's post happens to make it big on HN and they discover us through their logs, they can't give feedback while their posts is still on the frontpage.

2) HN has a long tradition of throwaway accounts [0] being used to give valuable input in sensitive discussions (abuse, corruption, medical, financial, family/social, or legally dangerous.) A waiting period means those contributions won't be made, or at the very least, won't be seen by the majority of readers.

The price of getting rid of drive-by trolling is that we lose these contributions. Seems better to just downvote or flag the trolls, and keep the really excellent stuff.

[0] There are some real gems among http://www.hnsearch.com/search#request/all&q=throwaway&#...