I fear that user rating systems are far too abusable. I can see allowing rating/moderation to be done by admin types, but if everyone has rating priv's the ratings start to get absurd in a big hurry. Don't believe me, just go look at slashdot and pick any (5, insightful) comment, then try to figure out what is either good, technically accurate, or insightful about the comment.
I also agree that editing is a BadThing. Not having any editing capacity or moderation provides a more solid legal footing if ever sued, or prosecuted over the content of a posting, such as misappropriated copyrighted information used without owners consent, or instructions for making nuclear/chem/bio weapons (apparently a lesser offense). As I understand it the lack of editing capacity defines you as a news carrier, which makes you largely exempt from liability with regards to postings made by users. Don't remember much detail (legal details rarely interest me), but I am pretty sure that this is something that has come up in several actions that were launched as harassment or retaliation against sites.
Regarding the quick scrolling, I find that the "recent activity" menu item is most useful for keeping track of new posts in threads that scrolled away. I haven't actually used the "hot list", but I think that allows you to effectively bookmark particular threads, so if you were using one for a reference this might be a good way to keep it around?