I think it has something to do with media player and browser combo. Every time I've had a reboot I've been playing music or had it paused and was browsing. I'm guessing corruption in mp3 file or some kind of resource conflict between the two because i also get stuttering on the track I'm playing sometimes when doing both.
Next time I get a stutter I'll look at the cpu/ram status bar icon and see if it shoots to the top.