....rare as in rocking horse manure?
Seriously, I have a group of cousins from up north that owned a beach house together in Cape May, NJ. In the northeast it's fairly common for families to own these beach houses, but more likely than not (as was the case with my cousins) there was a grandpa who bought the house long ago for a song, died and passed it down to the family. These houses stayed in the family with minimal problems because they were usually paid off when they were inherited; the season was so short (they're usually shut down for the winter); and there wasn't any of the wallet-draining HOA fees and gated community drama crappola like we've got today. I would never recommend family members getting together to "invest" in a beach house--too many moving parts to go wrong.
BTW, my cousins sold off the house in 2003 and now rent wherever they go on vacation.