a while after I got this Mac from work, I started getting plagued with all manner of crashes. they mostly seemed to be caused by (what seemed to be) really strange low-level issues, suggested by messages warning of EXC_BAD_ACCESS, and either SIGBUS or SIGSEGV. an example crash is below, from System Preferences of all things! I have only included the first part, for brevity.
Process: System Preferences  Path: /Users/USER/Desktop/System Preferences.app/Contents/MacOS/System Preferences Identifier: com.apple.systempreferences Version: 11.0 (11.0) Build Info: SystemPrefsApp-211000000000000~1 Code Type: X86 (Native) Parent Process: launchd  Date/Time: 2011-08-17 00:01:09.361 +0100 OS Version: Mac OS X 10.7 (11A511) Report Version: 9 Anonymous UUID: 5B3D93D7-29CB-4BE8-8762-265108DC7684 Crashed Thread: 4 Dispatch queue: com.apple.root.default-priority Exception Type: EXC_BAD_ACCESS (SIGSEGV) Exception Codes: KERN_INVALID_ADDRESS at 0x00000000d0000020
the problems even persisted after my Lion upgrade. it was starting to get extremely annoying, as I was losing work and context. I tried changing the RAM, uninstalling and reinstalling as many of the offending apps as possible, all sorts. I was absolutely loath to reinstall the entire machine, as I am sure many people are, when someone at work mentioned resetting the SMC and PRAM.
being a Mac newbie, I had no idea what these were, but this tip really did the trick. so if you are experiencing random EXC_BAD_ACCESS issues affecting just about every application on your Mac, give the above resets a try.