Doug: Thanks for the compliments! Some great shots from yourself too! Sharp eyes all round!
Maybe it's because I had to work so hard with my previous lenses but I actually found the 300 f4 comparitively easy to get it right with. As Brian quite rightly points out, very often a misfocused shot is down to the user rather than the camera but with the new lens, even on the converter, my hit rate has rocketed! Also, the ones that I miss now I usually have an inkling about even before I view them. With the previous big lenses I've tried on the 20D the focusing was erratic to say the least. I had the body calibrated by Canon, which did help a bit. Maybe that's why it's now so good with the 300 F4? What I also like is that they were all handheld - not had it on the tripod yet!
I personally find the 20D screen fairly useable for manual focus (not as good as the 5D though
). It does get harder as the light drops, of course. Brian, I guess that at an effective F8 max aperture then you are going to struggle in less than ideal light, both with visibility for MF and with shutter speed for freezing movement. There's also a chance I guess that you may have been seeing a slight motion blur as well as or instead of missed focus? (thanks for the input and the positive feedback, btw!)
I'll try it out with moving birds (hopefully) at the falconry this weekend then next week, if I can get up particularly early before work, I want to try and get over the hill to Chatsworth House (famous UK stately home, if you don't already know) to see if I can get some pics of the Deer herds on the estate. Thing is they only ever seem to be around when I DON'T have the camera in the car!