Well.. I'm of the opinion that you should get permission from people who are in photos to post them, period.. not just weddings. So, yes, I think it is rude to post pictures of the wedding ceremony and even parts of the reception before the happy couple has a chance to. Now.. pictures of you and your sweetie dancing at the reception? I think that's fine. But pictures of the ceremony, cake-cutting, first dance, toasts, etc. should be up to the bride and groom to post.
It may sound silly, but I think a big reason for this is that the first pictures posted get the most attention. So, if I post a picture of my sister's wedding, I know our mutual friends are going to "like" it and comment on it, and all the fanfare. If enough people do this, by the time my sister gets a chance to post hers, it's just not as special, and a lot of people would probably figure they'd already commented on my pics, so wouldn't bother. So I think I'd be robbing my sister of her limelight.
Also wanted to point out that the OP actually referred to pics of the bride and groom themselves, not of some of the situations that have been brought up in this thread. I think it's reasonable.
The female host (Mercedes) mentioned this as a "Cardinal Rule" of Facebook, and naturally I was curious about what everyone here thinks. Mercedes says that posting pictures of a bride and groom on FB is an etiquette issue, and the "rule" is that NO ONE in attendance at the wedding should post pictures of the B/G until the B/G have posted pictures themselves... and then, it's open season.