Recently, in the news, there was a post about a job listing on Google's site. They are apparently looking for someone with experience in "identification, selection, and negotiation of dark fiber contracts." Does this mean that Google wants to become an ISP?
While that might be kind of neat - A Google flavored ISP (after all I would imagine their rates would be cheaper than anyone else) - I don't see this as their plan.
Dark fiber refers to all that fiber optic cable that was laid in the late 90's but never activated, or was used but subsequently turned off. It's the stuff that no one is using now.
But for what purpose would Google need miles of fiber? Well, there are many uses.