Since commenting is such a huge aspect of these sites for me, I'll probably frequent HN much less often since I won't be able to participate in conversation. PARTICULARLY, I won't be able to get in the early comments that are necessary for making high-karma. You can't have your comment show up an hour or so later after "approval," you'll only net a handful of upvotes, because you'll be buried under the high-scoring top comments by senior HN users.

Perhaps make a mid tier, say 500 karma, where you can't endorse users, but don't need endorsement?