I had a kernel panic about 2 years ago, and another one a few days ago. I haven't had any other problems besides minor software bugs, and I was able to harmlessly reboot after both. I've been told this can mean many bad hardware-related things. Could it just be something relatively harmless, since it doesn't really seem too persistent? Is it worth having it checked out?
The first time you get a kernel panic, it is a reminder to make sure you have a regular backup system in place. Restart the Mac and check that your backup is configured. Check later that day to test restoring a files you need to be backed up.
The second time you get a kernel panic, decide how you're going to track when they happen. I use a 3 x 5 note card to document things like what I was doing when I noticed it in the date and time.
Other than that, until you lose real work, the occasional panic/error isn't a real concern as much an annoyance. If you end up annoyed or have recurring panics, gather objective data needed to solve most kernel panics. Apple documents their well engineered process for this:
Once you have a handful of events, checking with support is good since they are in a better position to weigh if hardware is suspected to be faulty or if your panics are software in nature.
Yes, sometimes a kernel panic can indicate bad/damaged or incompatible hardware. The frequency with which you have them is probably not indicative of a major hardware problem (i.e. bad cable connected to MotherBoard from HDD, etc.), unless you notice physical conditions that seem to coincide (i.e. hottest day of the year, child pounding on desk, etc.), or while performing the same software related task (i.e. clearing caches). It could be as simple as having one system file corrupted that is not often used.
On the other hand, I have also seen this caused by having hardware just lose its connection slightly (i.e. an eSata ExpressCard slipping out just a little while in use on a 17-inch MacBook Pro).
Twice in two years is nothing. Computers run on electrical signals not 0 and 1. Yes, sometimes errors occur. 'Single-bit errors' may occur, but the hardware and your OS are smart enough to deal with them most of the time. However, sometimes, they can't and you get the kernel panic, indication of something serious went wrong, perhaps not possible to correct. Twice in 2 years doesn't necessarily mean faulty hardware, just random unlikely errors.
If you are so worried about, you can start inspecting your hardware. Most kernel panics I have encountered were due to bad RAM modules! Start by running a memory test and see what you get.
There's so much conflicting and confusing advice on the web about Kernel Panics - and very often no reason to take your machine in.
Read Apple's own support page, About Kernel Panics , and MacWorld's How To Troubleshoot a Kernel Panic. You'll be able to isolate the problem and from there, know what steps to take, many of which are quite simple.