Sony has confirmed to us that, as with all previous PS3 models, the PS3 Slim's hard drive is fully upgradable, meaning you can swap out the existing 120GB for a higher capacity drive.
Over email, I asked Sony two questions: Is the Slim's hard drive still upgradable? And will Sony be supporting this upgrade option at retail?
Here's what they said: "Yes, the new model PS3 has a fully upgradeable hard drive. In regards to your question on support at retail, the situation remains the same as with the current model - it's up to the individual retailer to offer the upgrade service in store, or the consumer is able to do it themselves."
Good news while we wait for that rumoured 250GB model to hit retail.