Seems like I have found reason/solution of this problem
Hey! Thanks a lot for your suggestions. This might sound like a mystery, but it seems like someone else has found the source of instability, which was the bluetooth service... I uninstalled it two days ago, and I have not experienced any crash ever since. So, at the moment my system (Fedora 17) is running fine and stable... I will keep on monitoring it, and if the crash reappers, I will post an update here... However, so far so good. Thanks a lot for help!