When playing Skyrim on my PS3, it crashes after only a few minutes, forcing me to restart the system. I have 55GB of free space and no other games are having this issue.
I had many freezes and lost several savegames due to that crashes. After some research someone said, that the autosave-function is bugged. After turning this function off I didn't have any freeze or crash since 20 hours of gameplay. Aditionally the loadingtimes are reduced, because the game itself saves on every warp/quicktravel/whatever. So, try to disable autosave and maybe clean up the old autosave-files. Don't forget to back up all your savegames ;)
It isn't so much space with Skyrim. This has always been a frequent problem with Bethesda. Fallout and Oblivion have always had lagging / crashing issues. Sometimes it is just potluck whether it crashes or not.
I would suggest when you notice it lagging just stop playing. As in, don't move your character or select anything. Wait until the lights on the front of the PS3 stop flashing so much and then try moving forward with your character.
By personal experience, I know that when the PS3 is loading too much data (i.e. when the yellow light is flashing) the odds for a game to crash are bigger. I noticed that it happens several times in Skyrim, Fallout 3 and Fallout New Vegas (I hardly ever have such a problem in another games). I advise you to pay special attention when you enter big open areas. Every time the yellow light on the front panel of your PS3 start to flash too much and the game start to lag pause the game and wait about half a minute.
I would suggest deleting internal hard drive space, as that is not needed, or I would suggest getting a bigger hard drive. Another problem could be a bad disk drive. Hopefully this information will help.