Universal playlist interface

I want an anytime-anywhere playlist interface, so that no matter which music player or which machine or which device I'm playing music from, if I "favorite" a track, it is magically recorded to my has-it-all, omnipresent, cloud-like personal music database, such as one on last.fm or iLike.com. It should also know which source file I was listening from and how I can get back to it. I should then be able to pull up all my favorites into my iPod or like with a single click, and keep it up-to-date as I listen to more new music.

That was from the user side. With current proliferation of server-side music databases like last.fm and musicbrainz.org, this shouldn't be too hard to do. I see two hurdles: 1 getting all client-side software to talk on a single interface, and 2 getting all server-side databases to share information. The latter should be easier to handle as long as the services are co-operative and willing to provide an API, which any reasonable service today does. The first problem also shouldn't be too hard to solve either as long as you're working with open-source and modern software, but legacy commercial players like Windows Media Player and Winamp may be harder to write plugins for and, unfortunately, form a large fraction of user-base.

The sleek part of this exercise would be the universal interface, which must be designed such that it can make it's way incrementally and unimposingly into a user's music experience. Do you know of any such existing solution? Or do you want to build one? Life is too short and music too big to forget and lose a track you liked in the first listen.