I'm of the opinion (and have said it once or twice) that all accounts that are more than 6 months, or maybe a year, old that have 0 posts should be deleted. All accounts of this age that have 10 or fewer posts (or some low number like that), all of which are in threads they started or off topic posts in other threads, etc, should also be deleted. I realise this would be tedious and difficult, but I also think it would be well worth while.