The problem, while particular to the game's complexity and duration, may be rooted in memory management, according to pixel counting pros Digital Foundry. "The bottom line is that Skyrim is an unbounded game world running on a space-constricted system - and this applies regardless of the platform you play it on, hence reports of the PC version running out of address space and displaying solid colours instead of textures," says Tom Morgan. "The PlayStation 3 is unfortunate in that it's the platform with the most oppressive RAM issues (in addition to the split-pool set-up of the memory, the OS has a larger footprint than its 360 equivalent) so it makes sense that it has the most noticeable issues."
Said issues led to some disastrous framerate hiccups in Digital Foundry's 65-hour game ("It's the first time our performance analysis tools have ever recorded a 0FPS reading.") and inspired a warning to consumers from CVG. The latest Skyrim patch reportedly brings improvements, but DF suggests it may still become "unplayable for those with a huge time investment in the game - unless you're only willing to play Skyrim in half-hour bursts, saving and restarting the game."
We'd advise you to take regular breaks anyway, though we'd prefer if they were less motivated by the game breaking down. As usual, we'll keep you updated as Bethesda issues further updates to all versions of Skyrim.