Here are a couple of screen shots of the Xbox.com website showing the errors they are having...
The error messages respectively are:
The page requested requires your account to be gamertag linked. Currently, network issues are causing a problem retrieving your gamertag information. Please try back in a little while.
An unknown error has occurred. Please try your request again at a later time.
I noticed these errors starting to happen (as well as severly degrated site performance) at around 9am central this morning.
Hopefully Microsoft can get these issues resolved soon and testing can resume with Xbox Friends Thing so I can get it out to everyone.
[note] As soon as these issues are resolved at Xbox.com, this entry will be removed.