Same lense I use, and I agree with everyone that the autofocus is rather slow. But a quick flick of a switch and you go to Manual Focus and it works as fast as you like! The IS feature is brilliant..... for still or slow moving objects. Using it for a landing or departing aircraft doesn't quite work so well.....
That being said, having the IS feature on the D30/60 is a great option. Digital magnification of the image takes the 300mm out to 480mm so it gives you just a little more versatility in low light situations.
All you've gotta do now mate is get the Sigma 170-500mm baby! Now THAT is a fun lense!