This is what I know:
They have it at WL
It is $199 for up to five people, not any less if there is only 2 people. You have unlimited access to water mice, but I'm not sure what else, and you can only take the boats out an hour at a time, then you go back, if there is no one waiting to use your boat, you can go back out, but you do have to check in after an hour.
You do NOT have to be a guest at WL to d this, but I think you do have to be a WDW resort guest/on property.
That is all I know for sure! There was abunch of posts about this over on the resort board awhile ago and this is what I remember.
Maybe a search on that board could explain it better.