LEED 2012 (which is now renamed LEED v4, since it won’t be out before 2013) has loads of changes.
Since the changes apply to all different LEED rating systems, I am only going to mention the major changes and other changes that apply to all rating systems. If you want to see the detailed changes in a specific rating system (or in all), you can visit USGBC’s website and download a copy of the updated rating systems (with tracked changes highlighted in red).
So, for starters, LEED BD+C now has new compliance paths for Data Centers, Warehouses and Distribution Centers, and Hospitality projects. This is in addition to Retail and Healthcare, which USGBC added to LEED 2009 last year. LEED EB O+M now has new compliance paths for Schools, Retail, Data Centers, and Warehouses and Distribution Centers projects.