I wholly endorse "only allow comments to my entries for two weeks" as I have had the following things happen:

1) trolls going through my journal looking for any public entry anywhere just so they can comment on as many different posts as possible before I ban them;

2) F_W doing one of their "historical retrospectives" about some dumbass old HP controversy and people coming into old posts trying to start wankery up again.

The only thing I'd ever leave permanent open comments on is fic (for obvious reasons I think).