I won't tell you that it is worth it, in fact I think it is a big rip off personally. What I will say for it though is that for the most part it is a more stable on line platform than than I have experienced with the PS3 or Wii.
This being said, I was speaking to Scratches last night who was vey upset about what EA have done with Tiger Woods 09. It seems EA has now sold advertising in game and each hole you play is now "proudly" sponsored. As you pay for the game and XBOX live I think this is damn rude and will make me think twice before I purchase another EA title.
Unfortunately EA are not the only ones. Ubisoft added "current" movie posters to some of the online levels of Rainbow Six Vegas 2. I think they did the same with the Battlefield games as well??
Either way, If I pay for the game and the service to play it online I should not be bombarded with ads!