[amirmc]

I'm curious. Are there any other cases where one YC company has acquired another? Is this the first?

[oxwrist]

Certainly not the first. I remembered there's Loopt acquiring GraffitiGeo but I'm sure there's more: http://techcrunch.com/2009/10/20/mobile-social-network-wars-...

[jaredsohn]

From YC's first class, Reddit either acquired or merged with infogami (depending on who you read it from). http://news.ycombinator.com/item?id=20239

[nihaar]

Here's another example: http://techcrunch.com/2009/06/23/posterous-acquires-fellow-y...