Usernames. Yes, I know this one has been done to death, but there's never before been a good reason to actually do it. The old usernames (you know, those that haven't been updated in like 60 weeks or something). For instance, username "Joe". This guy hasn't posted a comment in his life, and stopped updating his journal 69 weeks ago, back in late '99. Does anybody else think that, perhaps, selling the username "Joe" would make some serious money? Perhaps do it over e-bay. Well, perhaps that one is a bad idea - he's got 16 entries, and it'd be kinda wrong to delete those so that some other person could get his username. But I've not got the time to go through highly desired usernames looking for a suitable user who has never updated or commented, and is taking up a good name.
I guess to do this, you'd have to go through all the usernames that haven't been posted in (or logged in to, or whatever, to avoid deleting people who solely comment), and pick out those that'd be worth something. For instance, username "James" has never posted a comment or an entry, and created the account over a year ago. And I just know that particular username would go for a high price (heck, I'd bid lots for it). Random alphanumeric strings aren't going to be wanted, so people with those names can keep them, but the people who've not updated and are taking up first names ought to go, and make LJ money by doing so.
Comments? Suggestions? Flames? One of these is unwelcome - see if you can guess which ;o)