I think it's a great idea, one that I'd bring to the reception, too. Put GoPro's on all the tables, and attach them to various adults and children to get pretty much all the perspectives. Just remember to bring 128GB cards, and loads of batteries.

And a rich uncle, of course. That amount of GoPro's isn't cheap.

Yes and no. There are a few stills from my own wedding outside of the formals that I love; hell, one of them I use as my standard profile pic on YouTube, Twitter, etc. Granted, you're looking at one shot out of fifty in those cases, a much lower ratio than from the formals, but it's still worth it to me for a photo of the crowded dance floor with my wife's cousin making the silliest face, his daughter on his shoulders; or the random video shot of my dad asking my grandmother for a dance and her face just lighting up.

ShadowDuelist, GoPros are a great "fire-and-forget" tool. As I said, we often use a couple during the ceremony for two reasons. First, the ultra-wide angle can give an impressive view of a majestic cathedral that you can't get on DSLR until you're getting a 14mm lens just for the job. Second, they can be placed relatively inconspicuously. In a church, as long as the pastor has no objections, they can be placed in the sanctuary facing out to get a shot of the gathered guests, in a pergola for a top-down view of the couple and the officiant, and even on light stands to get up ten, twelve, fifteen feet for a unique establishing shot angle. The high establishing shot is also why we have one as a dump shot during the reception. (It'll also double as a guest reaction shot when they're laughing during the toasts.)

I wouldn't use a GoPro, personally, for roving shots, whether intended to be used in motion or just going place to place. If you plan on moving during the ceremony you're better off with something with a nice long lens so that you can get closeups on the couple and maybe their parents in the seats, again for reaction shots. As for video booth messages, a GoPro would be too wide for one or two people talking into a microphone, but if you have a different camera for your main camera there it can provide a neat behind the scenes angle.

Tom's idea of GoPros on tables has merit, but as he said it'd be pretty expensive. If you were to do it at all, I'd place it on the parent tables during toasts, especially if you don't have an assistant videographer getting establishing shots for you. Also as Tom mentioned, battery life is a concern. A GoPro Hero 3 Black lasts for about an hour and a half, plus an hour with a battery pack on the back. Bring spares, especially if you have an hour long ceremony ahead of you. (Your battery should last the ceremony but you'll need to swap if you want to use it during the reception at all.)

I've seen video of a GoPro in the bride's bouquet but that's obviously a preproduction thing, designing the bouquet from the ground up to be able to hold it, making sure she's holding it that way forward as she walks down the aisle, and that the maid of honor holds it camera out during the ceremony (or if it's placed on the ground or a table, camera out). Invasive in preproduction and the bride needs to be enthusiastic about it, but not incredibly apparent to guests that it's there.

Another idea: GoPro on the toss bouquet

Vicar's Hat cam? Just throwing it out there?

Wait, if jesus was real, he'd be so be down with the gopro - He totally would have captured  himself walking on water with GoPros and tweet vid'd it immediately!

Interesting idea but man I would not want to be that editor

Yeah, low light on the Black series from the 3 on up is great. I haven't used it yet but I'm sure the 4 is even better.

I'm currently in the process of editing my wedding video, the best advice I can give is make sure you get a Norwegian and a frenchman to film it.