Thomcult: Sony has always occupied an awkward space in terms of mascots and emblems. Historically it has always been a logo-less (for want of a better phrase) brand. While Nintendo had Mario and Sega had Sonic the original PlayStation had, well nothing.
What Sackboy represents is a change of tone in Sony's approach to the marketplace, and one which the rest of the industry would do well to pay attention to. Namely, that the days of imposing top down meaning on consumers are over, that they are capable of defining their own fun and their own experiences. Along with Spore, Little Big Planet has the ability to empower gamers and let them fill it up with their own meaning and idea of fun - to allow them to act as inspired creators, rather than passive consumers - which is exactly what they want.