You know, this is one of the things that's really bugged me about the Xbox 360. (This and the whole "reliability" thing.) The console's Dashboard has always been terribly slow. In fact, if you want to really frustrate yourself in the middle of massively multiplayer deathmatch action on this console, just accidentally tap the Xbox 360 Guide button (the silver and green thing in the middle of the controller) and watch, horrified, as the Xbox Guide sslllllooowwwwwlllyyyy comes up on the screen, interrupting your game, and making you wait ever longer to dismiss it. The New Xbox Experience (NXE) didn't fix this issue at all. (Contrary to this stupid comment at Gizmodo: "Did anyone else notice? When NXE launched, it was pretty quick. But it's just gotten slower...and slower." Wake up, guys. It was never quick, and was always slow.)
Anyway. They're supposedly going to fix it.
During his last podcast, Xbox spokesperson/kind guidance counselor Major Nelson revealed that a "faster" dashboard update would be coming later this year with "a lot of very cool new features."
Hopefully, they really do fix it. Because nothing makes the Xbox 360 feel slower than clicking that stupid button by mistake.