I agree with both above posts. I thought guesting would be enabled in a week or so after launch, but it has been a month and it is not active. Some updated information about this would be very welcome. At least an estimate of when it could be implemented.
That said, if guesting is not going to happen, you will likely scare off a lot of players. GW2 is supposed to promote group play, but it fails miserably in this respect.
Random zergfest of players during dynamic events does not equal group play to me. Nothing social in that. Forcefully splitting previously established community by locking people to a server does not help either.