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So let's handicap the two, based on what we've seen so far:
Google has a very small chance of totally taking over the TV business -- which would be a massive coup -- and a huge chance of completely failing. (Sort of like its Nexus One phone was a big bet to disrupt the mobile phone industry, which wound up flopping.)
Apple TV, meanwhile, has a good chance of continuing as an obscure, niche device. But if enough people take a flier on the $99 Apple TV, Apple also has a solid chance of teaching people about the idea of using an Internet device in their living room, and it can gradually make the box more complex. This seems like a safer bet, if less disruptive.