one strange thing happened to me while travelling US. I have 60D with upgraded firmware to newest version (1.1.1) and I'm using magic lantern (1.1.1-ml-v2.3)
Everything worked fine up to the moment all my memory cards were full and I had to buy and use the new one (16GB SanDisc Extreme). After that camera started to behave very strange, sometimes it just won't trigger shutter, just lock up mirror and let is locked for 30s (I tried to "take a shot" without lens to see whats happening). And no file was added on the card (I was expecting at least the just black frame)
After restarting the camera few times and also removing the battery this behavior continued. Then I realized it could be software issue, because camera worked fine in life view mode (Av, Tv, P, M modes were not working). As the next step I tried to switch to another card, to see if it's not somehow card related. After putting full card WITH magic lantern files the camera went live again and everything worked fine.
When I switched the cards again, camera still worked fine (so no permanent issue), but I this situation happend 2-3 more times and every time using card with magic lantern helped to "unlock" the shutter. I also have to tell that only the new never used cards triggered this behavior.
FYI only - maybe might help someone.
Did it happened to someone else here?
Edit: added firmware versions