Pokertracker...useful?

[Shady Poker]

I am looking around for some kind of poker software to help me keep track of my stats and help me improve my game. From what I have been reading pokertracker seems to be the most praised software. Do you guys believe it is worth the price? Do you feel you have improved and greatly benefited from using it?

Also, does it tell you information on your opponents from the hands you have played with them or from every hand they have played? What are the other main features of pokertracker and what other programs do you recommend in addition to pokertracker?

Thanks a lot