In order to attain the highest quality images, the APO lens has been made using special low-dispersion (SLD) glass and is designed to minimize color aberration.
The above was searched out in Google within 10 secs and copied and pasted here. I know sometimes it's good to hear from others who have used it their experiences but I feel that outright questions like what's APO is meaningless. Might be more useful if you asked how does SLD glass improve your images and whether other users find that it delivers or not, AFTER you find out what APO is.
Your VR lens question is slightly better framed and I am sure a lot of brothers here will be keen to answer your question on whether they feel that VR or IS is useful. Well, depends on what you shoot. If you are shooting at the long end of 300mm, then VR is useful somewhat. It won't work miracles, but help maybe 1 stop (forget the 3-4 stops claims).
But then again, if you are shooting 300mm range, then it's mostly tele-macro or sports, and you should really be using a tripod anyway. Note also that VR doesn't work very well when cam is mounted on tripod,