I have been using this lens with my Canon EOS 40D at several air shows to photograph jets and propeller driven aircraft, the latter using shutter speeds of 1/320 sec or 1/400 sec at 500 mm (equivalent to 800 mm for my camera) using the optical stabiliser and have found that it gives superb results. You may want to reduce the shutter speed to 1/250 sec to give a slightly better blur to propellers and helicopter blades but I have not risked it yet.
The main problems with this lens, which many others of a similar specification suffer from, are:
Its weight - approximately six pounds with my camera - so you need a strong neck;
The size makes it difficult to use the zoom ring when hand holding it - autofocus is a must; and
If you are looking up at the sky and try to use the autofocus system when the plane is almost out of sight you will probably fool the system into thinking that it is nearer and you will have to refocus using a distant building or something similar.
The optical stabiliser is unlikely to work with a tripod so if you are going to use one you may wish to consider another lens e.g. the Tamron 200 - 500 mm.