Mojang | Support Center
The front help page now has indicators for each of the Mojang servers used for logins, server checks, skins, and accounts.
This is similar to the indicators we use on Our Worlds - servers, maps, claims, downloads
to indicate when the TOG server ports are active, courtesy of our generous hosts, Solutions First (see that page for details on how you can say thanks to them).
So if you have trouble connecting to our servers or simply logging in, you now can easily check Mojang's end.