Virtual idol sensation Hatsune Miku is finally set to get a game to herself, Hatsune Miku Project DIVA (provisional title), set to be released in 2009 for the PSP, and to be developed by Sega. The game is set to be a rhythm game, unsurprisingly (you were expecting an FPS, perhaps?), apparently with elements of interior design.
Some details, then: promised are a fully realised 3D Miku, strong customisability in terms of room design (the gorgeous looking Miku will apparently react to your choice of décor), various stages, etc.
The game itself focuses on timing, with the usual mechanic of being in step with the prescribed rhythm, and with successful timing comes a full tension gauge, allowing specials.
The game flow alternates between the rhythm segments and story segments, with something approaching a proper story apparently in the works.