While rebooting a Cisco 2960 switch to back out some configuration changes, I was not able to route traffic through the switch. After some troubleshooting, I noticed the following the error (with "terminal monitor" enabled):
 
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A quick search revealed this to be an IOS bug (actually 3 related issues). The switch shipped with 15.0(2)EX5 code. The immediate work-around was to power-cycle the switch instead of doing a soft boot (reload). The root cause of the issue is related to the "internal i2c bus" getting into a bad state. Once it does, the bus maintains power through a soft boot, so a reload does not resolve the issue. A power-cycle is required.
 
An upgrade to 15.2(2)E3 (MD) or 15.2(4)E (ED) or later will resolve this issue. http://www.cisco.com/c/en/us/support/docs/switches/catalyst-2960-x-series-switches/118837-technote-catalyst-00.html