You've seen enough "game within a game" things for LittleBigPlanet to make you ill. Gradius, Tetris, whatever, it's been done. But you haven't seen Lumines, especially one that comes from Q Entertainment.
Yes, Q, the creators of the original, have teamed up with Media Molecule and Sony to launch an official version of Lumines within LittleBigPlanet. It's due sometime this "winter".
UPDATE - Lost! In! Translation! Turns out this is just a LittleBigPlanet skin for the upcoming Lumines Supernova. Still cool, just not as cool. Sorry for the confusion!
今冬配信の『ルミネス スーパーノヴァ』が『LBP』とコラボ [Dengeki Online]