I noticed something interesting while resizing a SoundCloud.com browser window – there is (at least) a three phase responsive layout.
Phase 1 – Any windows under ~800px wide are a single column. Cross that threshold and…
Phase 2 – A second column pops up on the right. If you make the window a bit wider…
Phase 3 – The artwork on the lefthand column enlarges.
The Phase3 shift is the most interesting to me. I don’t think i’ve seen something like that in responsive layouts before.