Go pros are excellent for videos and capturing images in first person. If you pair them up with a second gopro you can then render 3D movies. Course now you're $600-700 into it.
They are light weight and you can't beat the HD images - especially for the $. Lots of kayak guys deploy them on the back and just let them run. They seem to run forever.
For snorkeling I don't see how you can beat it. Obviously you'll need the UW housing.
Now a couple cons I have - and these are strictly my thoughts. It's not much of a dedicated camera - if you want to have control (as I do), you won't have it. Whatever the camera decides to do is pretty much it. Also in the housing I believe it uses a 17 degree fish eye lens. So if you look closely you'll see that on the edges it's a bit "warped"/distorted.
I went through your thought process a year ago and here is what I did. I bought a canon g12 - this is a prosumer camera (just shy of a dslr). It has all the features I wanted of a regular camera - with full manual control. I then supplemented that with a UW housing - so there's no worries about getting it wet. I dive on occassion and it can go to 140' - somewhere I'll never go. Now this setup cost about $650, but I have an unbelievably good camera that shoots HD video and is underwater ready. The drawback to that is the cost and it's much bulkier than a gopro. But some of the photos I've gotten are unbelievable.
So that said, if you're looking to do first person videos complete with helmet cam - the gopro is fantastic. For the $ you can't beat it, but you get what you get. No control, but if it comes out fabulous - who cares. If you're asking can you go wrong with it - I doubt it, especially for dedicated video. Me...I'm a photo guy (not video).
Samples of G12 below: