Re: keying movement

if the footage is interlaced -> deinterlace before you pull a key (you will have twice the number of frames).
for keying itself: in general, pull a hard-edge matte, that is, you'll lose the motion blur, but get a solid (core) matte. then, pull a soft-edge matte. try to keep as much of the motion blur as possible. this will create a matte with soft adges, but holes, as well. combine the two mattes.
if you can't get a good key on the whole object as once, do it in parts of the object, for a period of frames, animate the key values,...
if after all, you still have holes in the matte, paint them out.

good luck,
rayk