Although Google I/O didn't bring us the finished version of Android Studio, we do have the first beta.
The new beta of Android Studio jumps the version number to 0.8 which feels as if it is getting close to a final release. But we need to keep in mind that Google has a habit of keeping software in beta for a very long time.
If you are already using Android Studio, then don't wait around for the usual update alert when you next start using it. The new beta has to be installed complete and there isn't a patch upgrade available. This shouldn't be a big problem, but it does reset your SDK setup. As you are also likely to want to install the new Android L API then downloading the whole lot again seems like the best option rather than making a backup and restoring the SDK.
If you have found in the past that upgrading using a patch generally involved having to upgrade gradle manually, you will be pleased to hear that future upgrades are going to be "nicer" and more backward compatible with your existing projects.
If you have been following the rapid rate of progress of Android Studio, you probably won't be surprised to learn that there is already an 0.8.1 update that can be installed as an automatic patch (and probably a 0.8.2 soon after...)
The new elements in the beta are fairly predictable. You can now create projects for Android Wear and TV as well as the preview of the Android L SDK. The build system has been extended to support projects that can be built for any of the targets.
The layout rendering also supports the new Android L theme and the new widgets and shadow layers. Another welcome addition is the ability to view the UI across not just different devices but different API versions. This is going to be very important as we transition to Android L and need to see what our apps look like on older systems. However, at the moment integration could be better. The new widgets aren't in the designer's toolbox and you have to find out how to use them. Presumably this will be fixed soon.
If you want to see what the Google team thinks are the important features check out this 45 minute presentation: