I remember Battle Net as the service that I logged into when playing Diabo or Warcraft II- but Blizzard has changed that.
The new battle.net web site looks to be Blizzard’s answer to Valve’s Steam Powered software; I was able to enter in my CD keys for Diablo II, Starcraft, and Warcraft III and they are made available to me for download- negating the need for me to keep the old CDs around. The games are downloaded via Blizzard’s client; the same peer-to-peer/direct download client used to distribute World of Warcraft updates.
I alsi merge my World of Warcraft account to use the same login as battle-net. Additionally, for those concerned about account theft, they offer use of the Blizzard Authenticator/Battle.net Mobile authenticator. The later is only useful (at this time) if you have an iPhone.