Well, you're right.
I still don't know what the problem is but it's not the 10k (now 33k) pull up on MCLR.
Apart from the PSU components (so that 5v and 3.3v are supported) there's only handful of components:
0.1uF decouplers on both sides of the chip VDD/VSS
0.47uf on pin 18, Vusb / RC3?
Resonator where it should be (no caps, included in resonator and we know the chip runs fine when burnt directly)
However, I've just noticed the reset switch connected to MCLR does nothing when pressed - the LED keeps blinking on and off. Surely it should freeze / go off and then restart?
There is something going on with this board that I must figure out but not now, as time has caught up with me. It could be something as simple as a poor joint / solder bridge
This is the board (from the well known auction site)
http://www.ebay.co.uk/itm/321294837918?var=510214454772 although he shows the older board with just the 5v power supply option.