Whilst I would advise against installing it just yet, daily builds of Ubuntu 12.04 (currently pre-pre-alpha) are available for download.
The build doesn’t sport much of a difference from Ubuntu 11.10 quite yet, although a raft of updated packages are in various states of implementation.
The release schedule for Ubuntu 12.04 is yet to be fully, formally and officially laid out, but expect to see the first alpha release of Pangolin sometime around December.