According to this Joystiq report, Diablo III boss Jay Wilson said at BlizzCon this weekend that you're going to be paying for some elements of the new version of Battle.Net, releasing alongside StarCraft II.
"We are looking to monetize Battle.Net so that we get to keep making these games and updating features," he said during a panel. "We kind of have to."
No date's been put on the update's release as yet.
More through the link.