(1)  The range is extremely useful.  17mm for view.  85mm for human head or upper body photos taking.
(2)  The structure is very solid.
(3)  IS is really useful.  I tried to turn off the IS to take a photos, and then turn on the IS to take a same view photos.  The different is pretty obvious. 
(4)  Good looking for puting in 450D. 
(5)  Have IS and USM at the same time.  It is difficult to have both in non-L lens.  Therefore, it is very good to have two both at the same time.

                        





