Has anyone developed a cross-os system to cache AssetBundles loaded via the WWW object?

All it needs to do it save downloaded assets somewhere in the user's library folder, check for cached assets whenever loading new ones, and delete old cached objects as necessary. I just don't have any experience with accessing user's library folders in a fashion that will work reliably on all OSs, so please offer your suggestions!

I'll release the caching system as a component of the Whirld 3 library once it is complete.

Background info on this topic @ http://forum.unity3d.com/viewtopic.php?p=241921