I've used the rpi-update utility to get the latest kernel and firmware to see if it addresses some USB errors. Following the upgrade the 'OK' LED is off most of the time and occasionally flashes on. The Pi appears to operate normally. I've done this with two SD cards, each behaves the same. If I flash them back to the state I had before the update, the LED stays on.. My installation is fairly standard, just the April Debian and a VNC server. The version details after update are :
Linux version 3.1.9+ (dc4@dc4-arm-01) (gcc version 4.5.1 (Broadcom-2708) ) #101 PREEMPT Mon Jun 4 17:19:44 BST 2012
Has anyone else observed this behaviour? Should I be concerned?