I recently bought the 70-300L refurb. I should say I am really impressed with the lens. I had the 70-300 Non L, not sure if it was the copy I had, at the longer end, the images were usually soft. I then tried a 100-400L from CPS. that lens was awesome. the push pull feature was a problem initially, but then I got used to it in a few hours. But that was pretty heavy and long. I did not see myself packing it to take it with me most of the times. So I decided to get the 70-300L, heard some good reviews. It is well built, but not so heavy, very hand-holdable, short enough and good glass too. I took it to the zoo and the main thing I have to say about this lens is, it is SHARP!!!!.
It is more versatile on FF Camera on the shorter end.
Some pics below. I used a EOS 40D for all the shots.