We have a full moon this weekend, so I'm getting comfortable with my 2x TC hooked up to the 80-200. I think this 100% crop came out quite nice, actually. The 200mm lens with a 2x TC mounted to a D90 with a 1.5 crop factor is like 600mm on a full-frame body.

Nikon D90
Nikkor 80-200 f2.8 @ 200mm
Tamron AF SP Pro 2x TC
ISO 100 (Lo 1.0) @ f5.6 for 1/160