Update: We've now been told that in-game XMB in being checked for full library compatibility and that user-music and Trophies will only work with games created with the brand new tools. More here.
Update 2: The release is now rumoured for June. We're waiting on comment from SCEE.
Videogaming247 has it on good authority that the upcoming PS3 Firmware 2.4 will include in-game XMB and Trophy support.
We're told that the added XMB feature allows users to play their own music in-game.
Programming tools to support the update have apparently now gone out to developers.
We're unaware that a release date for the software has been set. Sony has already said that in-game XMB wil be added to PS3's functionality this summer.
This is unconfirmed. Just remember where you heard it first.