Jogger: if youve got an 18-50/2.8 it makes more sense to get the 70-200/2.8.. the 50-70mm difference is nothing and can be made up by walking. the extra 225-300 on the tele end is far for useful.
70-200 on a film body eq 50-150 on a dx wrt FL. 70-200 is a classic range but for FF. but DX shooters need something on a similar range and halp the price make it interesting. but i am not going to sell my 70-200 VR2 for a 50-150 OS :)