In order for your app to take full advantage of the iPhone 4 Retina Display, you'll need to add 2x resources to your iPhone project.
If you're using SVN to manage your files, you'll be faced with something pretty annoying:
$ svn add xunYi7/library/images/blackArrow@2x.png svn: warning: 'xunYi7/library/images/blackArrow' not found
This was incredibly frustrating for me, no matter how I tried to escape it: single quotes, double quotes, backslashes, etc. SVN refused to add.
This is due to internal path recognizers in SVN. It expects the last at symbol to specify a revision. This is easily corrected by adding an at symbol to the end of your file:
$ svn add xunYi7/library/images/blackArrow@2x.png@ A (bin) xunYi7/library/images/blackArrow@2x.png
You'll still need to manually add each resource, but it's better than nothing. You could also use an IDE like Cornerstone, but I prefer the SVN CLI way of managing SVN.