Yesterday I upgraded the Shoutcast Mumble and main 1.2 Mumble to the new 1.2.3 version. It’s a prerelease version, so it might not work perfectly.
The main feature this new version has is built-in recording. If you don’t need the recording stuff, you can just stay on the 1.2 stable version, there’s no reason to upgrade. If you want to record your or your team’s ramblings, get the 1.2.3 developer snapshot from the Mumble website.