If you experience the problem that your mac freeze after one or two hours of usage, you shouldn’t blame Apple, if you’re using a SSD: I’ve found this entry. The error came up from a firmware error in the Crucial SSD. So I went to the Crucial homepage, burned the ISO-File onto a CD and boot from it (on mac you need to press the ‘alt’-key to get the boot menu).
And voila, after a reboot all was working again…