"hello world" with 18f6680

[skimask]

OSC1-OSC2, it shows 0V
OSC1-GND, it shows 2.5V
OSC2-GND, it shouws 3.6V

OSC1-2 - should show more than that, but your meter probably won't respond quick enough. Got an AC setting you can try?

OSC1/2 - GND - both sound good to me.

In your schematic, is that a 20Mhz resonator, crystal?
Try changing your config's to use a different type of clock, R/C, external, whatever, see what happens.