I've got an 8MB cache drive -- a Western Digital 120GB Special Edition. I have to say, this is a mighty fast hard drive, and would perform great in a video-editing setup. However, for just storing photos and music and such, you won't see much benefit with the extra 6MB of cache.
It would be perfect in a web server setup, though, as the cache is best utilized for multiple, fast, small read operations. The cache basically keeps information about recently accessed files, and the 8MB cache just offers more space to store more frequently accessed files. In the right setup, it does offer a decent improvement in speed. For a home user, save yourself $50.