Stop being careless with your users' bandwidth. Assuming that every client should get the highest-resolution (and thus highest-bandwidth and highest-memory-cost) assets is just lazy.
Use Javascript. Something like https://github.com/scottjehl/picturefill works beautifully and results in only one request per asset, with a noscript fallback. It's more markup, which is kind of a pain in the ass, but it means that the right clients get the right assets and you don't end up destroying your poor EDGE and 3G customers because you decided they needed a 2400x1200 splash image. Let's not forget that a "retina" image imposes a 4x memory cost on the client - image data has to be decompressed to be displayed. So, your user on their mobile phone with 512mb of RAM is going to have a terrible experience when your website is using 4x more of their precious RAM on images that don't actually provide them with any visual benefit.
Double-pixel displays are still, by a massive margin, the exception. Unless you're specifically serving a Retina Macbook-targeted audience, you're going to incur a lot of overhead for no appreciable benefit for the majority of your audience.
Not to mention, using high resolution graphics when only displaying at a lower resolution increases battery usage and lowers performance of the webpage.
Stop being careless with your users' bandwidth. Assuming that every client should get the highest-resolution (and thus highest-bandwidth and highest-memory-cost) assets is just lazy.
Use Javascript. Something like https://github.com/scottjehl/picturefill works beautifully and results in only one request per asset, with a noscript fallback. It's more markup, which is kind of a pain in the ass, but it means that the right clients get the right assets and you don't end up destroying your poor EDGE and 3G customers because you decided they needed a 2400x1200 splash image. Let's not forget that a "retina" image imposes a 4x memory cost on the client - image data has to be decompressed to be displayed. So, your user on their mobile phone with 512mb of RAM is going to have a terrible experience when your website is using 4x more of their precious RAM on images that don't actually provide them with any visual benefit.
Double-pixel displays are still, by a massive margin, the exception. Unless you're specifically serving a Retina Macbook-targeted audience, you're going to incur a lot of overhead for no appreciable benefit for the majority of your audience.