How Many Web 2.0 Services Have Gone Mainstream?
centernetworks.com
centernetworks.com
I'd say that's about it...those are the only ones where everyone knows what they are because they are constantly talked about in the mainstream media
These are ones we know because we are in a western society. There many other big hits in other countries that we have not heard of as they are not reported by western media e.g. until recently I never heard of shaadi.com and thats a big Indian player with a western bias which only gets reported as it is in English language and also doing well in English speaking countries
There are many more big players in China, Russia etc., all depends on what your assessment criteria is as they did not mention that in the article.
Ebay, Amazon, Cragistlist? and with the plethora of dating sites out there, theres a couple that could be considered "main stream"
Finally, as much as I'm not fond of piracy, you'd probably have to put The Pirate Bay in with that lot too.