Well,

Everybody is asking for it, so I will too. Sync!!!

Not sure how this would work necessarily. Maybe to dropbox? Itunes on different devices is a good example, but apple has the cloud and tons of servers to make this happen. The back-ups are small data files, so if everyone's forum account could also be their account for syncing, this should be pretty doable.

What if you could only sync playlists? This way the playlist when it syncs, only adds songs, never deletes them from whatever device you are syncing too. So a key function/attribute of sync would be that it only syncs new data, never deletes old data. Then just add some functionality to the songlists on all devices so its easy to search out duplicate songs and only keep the most recent one (last edited).
I understand that its possible to do this now with some dropbox manuevering;however the problem I am running into, is that when I open my playlists on different devices, I forget which one is up to date, and likewise with songs.

~Ben