I realise this isn't a major issue, but it's an annoyance. If for any reason I get disconnected from Live - let's imagine say, my cat pulls the power cable out of my router or some other more plausible scenario, such as a temporary (sometimes only 30-60 seconds) internet drop - I am unable to use the 'Connect to xbox live' option from the main xbox dashboard menu. I have to completely sign out of my profile and sign back in. Otherwise, I simply get the 'failed to connect to xbox live' message.
As I said, it's not a major issue, but when playing multiplayer online games which are linked to your profile, it means it takes that much longer to get back into the fray, which can also sometimes mean missing the boat when you were queueing with friends.