what on earth can I be doing wrong?

[skimask]

Make it even simplier:

trisb = 0
main:
portb.0 = 1
pause 500
portb.0 = 0
goto main

No variables, no nothing to mess with anything...

And strangely, my logic probe records a high on RC6. Which is strange since I don't think I've bothered with Port C in any way

It's floating... All (ok, most) pins are set to input on RESET so they don't load down the external circuitry (well, that's one reason anyways). So, it's probably floating. I'd be willing to bet if you put a 'scope on it, grounded out the pin with a 1k resistor, it would go to 0v, then when the resistor was pulled away, it would rise 'slowly' back up to 5v.

Or have I found a brand new way to be confused?

Yep...you have...
Do a search on config bits and presetting, etc. There's a bunch of threads on presetting config bits and clock settings, etc.