Well Plenty of Fish seems like a good target, bad design/UX makes it vulnerable Vault and eBay are another two examples. What these all have in common is requ

Well Plenty of Fish seems like a good target, bad design/UX makes it vulnerable Vault and eBay are another two examples. What these all have in common is requiring a critical mass of users to work, which gives them a barrier to entry that allows them to become complacent.