Well MGS or the mainstream FF series could be considered Sony's "killer app", although they don't appeal to nearly as broad an audience as Mario, despite selling millions of copies each. I think Twisted Metal is going to claim the title later this year/next year/whenever.

LBP has had me interested for some time now, but depending on what other games are released at the time, how good of a vibe i get from the demo/rental, and the pricing will determine if I buy it. I'm not really into paying $65 after taxes on novelty games.