Welp, looks like Battle.net is down again - or, should we say, won't be the same ever again.
Blizzard's looking to rebrand their Battle.net service to unify the branding behind all of their services. They've already started to do this with the Blizzard Voice and Blizzard Streaming services - now the client we've been referring to as Battle.net will no longer be called that.
"When we created Battle.net, the idea of including a tailored online-gaming service together with your game was more of a novel concept, so we put a lot of focus on explaining what the service was and how it worked, including giving it a distinct name," Blizzard said. "Over time, though, we’ve seen that there’s been occasional confusion and inefficiencies related to having two separate identities under which everything falls—Blizzard and Battle.net. Given that built-in multiplayer support is a well-understood concept and more of a normal expectation these days, there isn’t as much of a need to maintain a separate identity for what is essentially our networking technology."
Be ready to ask for people's Blizzard Tech ID rather than Battle.net - though I'm sure most will still give you their battle.net ID anyway.