That title is a little biased, its not like the STB has permeated american households already. Whether you are talking about consoles like the PS3 or the Xbox 360 or the STB used by every digital cable and satellite provider, the STB is pretty pervasive, or is that invasive? However, with the possible exception of Tivo and maybe WebTV, these Set top boxes have rarely ever fulfilled on their promise. If its the Ps3 or the Xbox 360, they are 95% games and 5% "other" so they can't really be seen as a success as a set top box.
Lets consider the benefits that Google has going for it, if it were to make a set top box.
1.) Open Source: Any feature currently available on any DVR has been aped by open source and in a lot of ways, trumped. Using MythTV for example, you can automatically cleave commercials from your recording based on subtle cues like a complete black screen before and after commercials and the fact that the Channel bug ( the station logo on the bottom of the screen ) does not appear during commercials
2.) Google: Google has content through youtube and they can get you just about any other content using reader, news and of course search.
3.) Broadband: with 7mb or faster DSL becoming standard in many homes, I beleive that now is the time where IPTV could really take off.
What does Google have going against it?
Who would make a Google Powered TV box? I don't know if a redressed PC on top of your TV is enough for Google, they need to make a reference design that isn't just X86 with a different wrapper. Take a cue from Apple, who is now making their own CPUs or find a partner that isn't the perpetrator of the Beige Box blahs.
Either way, Google knows what they are doing, they understand their audience and they have the capital and the Brain trust to be able to bring it together into a true, set top box.