Had an unexplained reboot using the SDHC kernel - no idea why, I just found the N800 stuck at the "Nokia" screen after I'd left it idle and on battery power for a few hours. Have rebooted, it's recharging now as the battery was almost finished - probably not related to the updated kernel as there have been so many reports of random reboots, but thought I'd mention it. Will keep an eye on it and post again with updates.