I almost always use this website when I’m playing a Xbox game. (Yeah, I love achievements) Some games have various collectables and sometimes people create interactive maps for them. Such as Dr Mong’s Bioshock 2 guide. It’s great to have on your cell phone because it’s easier to have with you on the sofa while playing console games.
I’m a bit amazed that there isn’t an app for X360A or PS3T. According to their forums it’s most likely due to resource constraints. It would be perfect to track your Achievement progress and have the guide available on the phone.