I gave TPG a call, they did a few checks then asked me to reboot my modem, so I removed it's power for 10 seconds, then waited the 5 minutes until my line came back up.. as usual, the line took an age to sync, then rock solid, speedy intermenets again... and I only waffled at the poor tech support chick for about half that time before deciding to just leave the support ticket open until I call back... thanks Patricia, we're working again.. TPG rock


So yeh, she explained the connection had clocked up quite a few errors and that the modem reboot resets all that.. nice to get useful, informative support.
For anyone interested, I'm running my second officeworks-purchased Netgear D834G, a modem I get great results out of, and always behaves snappily both from internal and external requests. It also includes a 4 ports switch, which our linux (mta) server hangs off, and a wireless router, which I am communicating from this laptop via.
I would suggest any issues that caused the outage, in this instance, are more likely the Telstra dudes I saw in the hallway the other morning, than any unusual degrade in performance of the router I know and love.