...and now they're back. This time with the added bonus of it sometimes staying on the colored "koboarc" splash screen for nearly a minute before switching to the confetti stream animation.
Hmm. Starting to think it's might be Twitter's fault - I normally have it up, even when the Arc's idle (which is when most of the reboots have happened). One of the reboots was while I was in Google Currents (but Twitter was in the background) and two of the others when trying to refresh Twitter.
EDIT: Reboot 2... (9:20am)
EDIT: Reboot 3... (9:26am)
EDIT: Reboot 4... (11:15am; this time Twitter wasn't even active, at least not on the multitasking list)
EDIT: Reboot 5... (3:40pm; had it off for a couple of hours while out, so uptime about an hour and it rebooted when I was swiping away Twitter)
EDIT: As for using logcat, I've no idea how to get the SDK up and running (and the Arc recognized properly) to be able to start running adb commands... :/