Sony has today published an update to the firmware - version 3.21 - which removes the option to install other operating systems (OS's) on Playstation 3 This option has typically been used to install Linux on the popular gaming console.
If one accepts the update from Sony, all data on existing Linux installations on PS3 deleted - and can not be accessed again. The ability to create new Linux deployments are equivalent removed as you can not go back to the previous version of firmware.
If you are not installing the latest update from Sony, you lose the ability to access the PSN Store to play some new games and the latest Blu-ray releases.
The reason for this drastic action from Sony's side would be that a hacker has gained access to all parts of the PS3's hardware and software and thus have the opportunity to publish a three-party firmware - as seen for the Iphone, Wii and Xbox 360 - which enables Piracy of games. The attacker recommend all PS3 users that they are not installing the latest firmware - but that as a PS3 user, rather than waiting for his publication of an alternative firmware. See more at PS3 Hacks.
The latest update affects only the "old" PS3s. PS3 Slim has never had the opportunity to install an "Other OS".