The main concept is the same, isn't it? The execution and branding vary widely, but that's exactly the point. Like Youtube vs. Google video, this example shows that, even here, first mover advantage doesn't count for too much.
You can't really call vastly different sites the same idea. This train wreck totally misses the "I would show this to my friends design" aspect of the idea:
http://web.archive.org/web/20010202080600/http://amihot.com/
And you've got to admit that the basic idea alone totally carried the hotornot site.
edit: archive.org confirms it. You've got to be kidding me if you think those sites are remotely similar except for one tiny feature.