G!

Looking at the new google interface one indeed may wonder what was google thinking.
One of the important factors of google clean interface was the it worked so well with their advertising system. Are they looking for a way to remove the attention from the advertisements? I don't think so.
However, with the Android and Chrome OS coming out I think another explanation is possible. Google is looking to expand it's application market. While still a leader is search, it is behind Yahoo and Microsoft in actual users. While Rupert Merdoch's threat to cut off Google seems laughable, it does highlight the fact that google has one main source of revenue, ads. This source is dependent on content created by others and indexed by google. If the raw material used by google will become more scarce, so will it's value as an advertising platform.
Chrome and Android fit nicely into this model, in the same way the Microsoft office suite and Windows Mobile fit with Microsoft Exchange and the iPhone fits with iTunes. Go and SPDY are additional steps in the same direction - creating a Googlesphere.
My guess is that the prime target at this stage is not Microsoft, but rather Yahoo, or rather it's userbase and content base.