To elaborate, for anyone who hasn't used Photoshop (in several years): you can have layer groups which act as folders containing several related layers, so when you're browsing layers, it isn't just a mess of 500 some-odd rows.
Depending on how hard the PSD format is to grok (purposefully or otherwise), this may be nigh impossible, but it also seems like it would be a great exchange format (which may be a another reason Adobe wouldn't want it). Then again, maybe there's already something like this...?