They'll do the job for the next 5 years or more. In 2005 a 360 was significantly cheaper than an equivalent PC and I'm sure the same will be true this time around.
If you look at how the extra power on PC is used you'll see it's the same type of games, prettier. Almost universally. I can't think of a PC game that uses performance to do something significantly new or interesting, or even do some gameplay better.
It's going to be the same this new generation too. What can we so with this extra raw power? Not much more except make the game games, prettier. Sony, Microsoft and Nintendo know this, which is why they're all pushing for second screen integration, social features, online connectivity and (especially in MS's case) motion input.