The next firmware upgrade for Playstation 3, v.3.21, that will be out April 1st will remove the ability to install other operation systems on the machine. The reason is said to be security related, with some pointing out that this sounds a lot like the language used by Sony in relation to the PSP (which has been plagued by piracy since the start).
Sure, you can decide to not upgrade and keep your Linux OS; but then you'll end up with a machine that can't connect to PSN and risk locking yourself out of games that need v.3.21 to play (which, we suppose, will be more or less every game released from April and forward). If you have a Playstation 3 Slim, this update won't change much since you can't install another OS on it anyway.