[gerrit]

The user experience when viewing webpages is improved by actually showing a lower-resolution image while the crisp high-resolution image is being downloaded (however slowly), similar to progressive JPEGs.

Depending on the data contract, the user experience when viewing their mobile phone bills might be affected negatively though.

[downx3]

Would it be better to sniff the header?

Accept: RETINA

Something like that, at least then you could turn it off in the browser.

[downx3]

Might be just as well to sniff the user agent.

[goatforce5]

Is there a difference in the user agent between iOS 5.1 on a 3GS and a 4S?

[downx3]

Thought it might be better to sniff the device resolution, but apparently the ipad3 lies!

http://www.priteshgupta.com/2012/04/detecting-ipad-3-for-spe...

[ryannielsen]

The iPhone 4 and 4S also "lie". It's not really a lie, though. The displays are intended to have higher pixel density, not more screen real estate. By reporting the "incorrect" size, websites are actually sized consistently across all generations of iPhones and iPads, but the retina devices render the same content with higher resolution.

PS: you may wish to add a "(-webkit-min-device-pixel-ratio: 2)" clause to your media queries if you want to target retina devices.

[mnutt]

Not that I can tell, unfortunately.