I just grabbed a FiiO X3 this week and i'm very happy with the hardware quality of things but i do have a few gripes with the software!
* No Playlist Support. Gotta have at least M3U support. I want to be able to create playlists and copy them to the device like an iPod
* Ability to customize the main menu, some things are unnecessary.
* Being faster with skipping tracks. Compared to a Classic iPod with has a standard hard drive in it, i've noticed the X3 takes a bit longer to start playing the next track.