Morning mate, apologies for the radio silence, got home to be faced with a sick baby and stressed mrs. Not really the politically safe thing to do, jumping on t'interwebby and trying to sort a phone out!
Anyway, I reformatted the data and sd-ext, then immediately after that reflashed GV 1.5 and the Gviollet HAVS AXI kernel. Things ran ok for a while, I then flashed BlueVillain (?) Theme and Circles Mod, and updated BusyBox to 1.18. The problem then happened again.
So. I have nand restored Defrost which I started the week on. I'm going to leave this a few days to see if the phone plays up again. If it does then I guess I have a hardware issue. If it doesn't though...? GV problem or still a problem with my SD Card / partitioning?