From the developers of Path:
To the engineers in the crowd, we’ve open sourced a bit of code that we use heavily in Path and that you might find useful in your own projects…Fast Image Cache is an Objective-C library that—you guessed it—caches images fast. Use it to cache like-sized images (e.g. profile pictures, photo thumbnails, etc.), persist them to disk, and display them without the overhead of opening files, decoding image formats, or even really copying memory.
Fast image cache is available on github.