When playing Wow, you can have a better performance if you are in a team. If you were in five-man, ten-man or twenty-five-man content as a shadow priest, working as part of a team would be your major focus. DPS players tend to fade into the crowd as the least important aspect of any raid encounter, so you should contribute to the team work as much as possible. If you are an elemental shaman, you can use Wind Shear every chance you have.
As for shadow priest, putting two points into Improved Vampire Embrace was an easy call. However the talent will disappear in Cataclysm and you should have a close look at new talent or ability that might take its place. For a time, I figured that ability could be one we already have, Silence. It seems that the team still keeps it gated behind a two-point investment in Improved Psychic Scream.