Idea for pg: Consider preventing accounts under a certain age (and/or karma) submitting stories. The limit could be really low (say, 24 hours and/or 5 karma) and I'm guessing it'd knock off 90% of the spam/trash problem..?
I would personally feel that that wouldn't help as much, as many of the new accounts are just people wishing to express their (perhaps unpopular) opinion without putting their main account and thus themselves in negative light.