Tried to load the responsive example on my Galaxy S3 and my co-worker's iPhone 5 and it looks exactly like a large desktop window where the two items are side-by-side.
Quick experimenting shows that adding a meta viewport tag with initial-scale=1 should fix this problem (you don't need to also add things like width, minimum-scale, etc. that you often see in meta viewport tags, just the initial scale). Without this initial scale, the devices are reporting back their actual screen width, which may be well over 720px for high-end devices.
Tried to load the responsive example on my Galaxy S3 and my co-worker's iPhone 5 and it looks exactly like a large desktop window where the two items are side-by-side.
Quick experimenting shows that adding a meta viewport tag with initial-scale=1 should fix this problem (you don't need to also add things like width, minimum-scale, etc. that you often see in meta viewport tags, just the initial scale). Without this initial scale, the devices are reporting back their actual screen width, which may be well over 720px for high-end devices.