It's happened in three different applications.
First application was with Elgato's EyeTV.
Second application was actually Quicktime.
And this morning it froze while I was watching a video on YouTube using Chrome.
It only started happening last night, so i haven't had a lot of time to test it, as every time it happens, I have to force the computer to switch off with the power button, which I hate doing... It just becomes completely unresponsive.
I've verified and repaired permissions using the disc utility, but the Verify disk and Repair disk options were greyed out and unavailable for some reason.
I've also done multiple fsck's in single user mode at start-up to check for and repair any problems, but it's still doing it. I haven't done this using a recovery disc yet though, as I haven't had time.