Funny that this thread should be sitting here waiting for me. I just got a Tamron AF70-300 f/4-5.6 that I use on my Rebel XT DSLR (which makes it more zoomy, I am told). The first thing I tried it on was the moon with a tripod & setting it on a timer so I wasn't touching the camera. This is the best shot I got (totally unedited, just cropped):
Exposure: 0.05 sec (1/20)
Focal Length: 300 mm
ISO Speed: 400
Exposure Bias: 0 EV
I'll try playing with it in the Gimp & if all goes well try some more shots tonight. Great topic! Thanks!