[Update]Microsoft has sounded the all-clear with regard to sign-in issues. However, it seems that other parts of the service are experiencing problems. According to Microsoft's Xbox Live status page,
"We are aware of an issue members are having sending and receiving messages, seeing friend's statuses, sending or receiving game and party invites, and accepting friend requests on Xbox LIVE. We are currently working as fast as we can to get this issue fixed, thank you for your patience during this time and we will update you with any new information we receive."
[Original Story]
My own attempts to sign into Xbox Live have proven difficult, and the official Xbox support Twitter account tweeted that is working to resolve the issue.
It's never a good time for Microsoft's Xbox Live service to go down, but the timing is especially bad right now amidst rumors that the next Xbox will require an always-online connection - something our readers are not happy about.
We'll be sure to post an update when Xbox Live's issues are resolved. You can also check Microsoft's official status page.