As reported last month, the code for Google +1 buttons could be improved so that the buttons load faster and stop blocking other resources. Google updated the code and recommends publishers to generate a new code.
Google also optimized the existing code so that the button renders up to 3 times faster. Even if you don't update the code, you'll still benefit from these changes.
The code generator is easy to use and I've noticed that a lot of sites added a +1 button next to Facebook's "Like" button. It's unfortunate that Google didn't optimize the code when it was released.