Blizzard has unveiled a new design for Battle.net complete with new features and functionality. The development of a "new Battle.net" has been hinted at for a long time in anticipation for the upcoming releases of both Starcraft II and Diablo III.
The new Battle.net is an upgrade to all preexisting Blizzard Accounts tied to Starcraft, Diablo 2, and Warcraft 3. Owners of World of Warcraft have an option to merge all of their accounts to the new service.
Be sure to check out the new Battle.net Account FAQ too, as it may answer many of your questions regarding the new system.