Autodesk has released a Service Pack for Maya 2011. Download it from the Autodesk website.
Please refer to the readme file for the complete list of issues addressed in this SP.
Remember each release is cumulative; it contains the fixes from the Hotfix(es) that preceded it.
Note: You will also need to update your installation of mental ray Satellite and mental ray Standalone to benefit from some of the fixes in this release.
If you have already installed the Maya 2011 Subscription Advantage Pack, you do not need to install Maya 2011 Service Pack 1, since it is already part of the Subscription Advantage Pack.
For a complete rundown of what's new in Maya 2011, please refer to this post.