Well, something's been happening today when I was at work!
My logs show multiple T3 and MDD timeouts, as well as the following: TFTP Request Retries exceeded, CM unable to register.
That, and my downstream power is down to around 0dBmV from 4ish, and upstream power to 48dBmV from 40ish. So I think there was either a fault or someone re-jigged something in my area.
This area has always been good for speeds, but a quick test on TBB and Speedtest show it easily maxing out at 107mb on the downstream. In fact I've never seen such a flat graph from either test before. Not bad for peak time.