The Cell's Size & Performance Has Been Improved In The PS3 Slim.

The electronics giant have confirmed that the Slim's new Cell is "manufactured using an advanced 45-nanometer manufacturing process" that will deliver "many performance improvements while drawing less power than earlier chips". These chips are obviously cheaper to produce and, in part, are responsible for the smaller and more power effective Playstation SKUs.

There are also rumours that the new Slim "adds hardware enhancements that make it speedier", although it's unlikely these upgrades will ever be noticed in games, due to gaming systems being designed to a specific specification. However, if they help the XMB to load that bit quicker, it would be neat.