Well, is your internet stable? no slowdown?
do you feel your connection to the 360 slow?
try clicking on friends and see how fast their gamepics/info generates, then press B to see how fast it goes back to the dashboard.
if it's more than 15/20 sec at max, then there is something fishy with either your connection or MS servers.
NOTE: Also open NAT and UPNP on your router, it could help.