I've been reading up a bit onthe subject lately, and talking to some industry friends about the subject, and I have to say the policy that makes the most sense to me is this:
(1) Lifting the "opening night" embargo on theatre reviewrs. It just makes no sense in this day and age, really. Reviewers aren't going to see the show again after opening before writing their reviews. Reviewers see very late-in-the-game previews anyway, and "opening" has as much to do with union regulations (You can't give notes after a show opens except to maintain the show etc.) as anything else. So let's just lift that embargo and let reviewers publish their thoughts whenever they feel like it.
(2) If a blogger is going to be invited in some kind of press capacity (which I think is a good thing) they should be invited to press previews, and see the show and be treated basically like press. I don't think regulating who those bloggers are via some central entity makes a lot of sense. Press departments will build relationships with different bloggers, and really it's their perogative to invite whomever they feel like.
(3) But that's if they're being given free tickets. Really, nothing can be done to regulate the blogosphere. People will see a show, react and post, and there's nothing you can do about that. So for those who pay to see a show, you really just kinda gotta leave it alone.