I'm not really clear on when a meme is a meme, some of these seem to just be popular sites. The Wikipedia article on the subject is horribly dense, and it's hard to pick out exactly what the defining characteristics of a meme are.
Personally, I'd call these "fads". Although the concept of "meme" is connected to the concept of "gene", and I swear that the hamster dance has a life of its own...
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