While Visual Studio 2012 looks forward to Windows 8, it doesn't shrug off its ancestry. The IDE is particularly tolerant of projects built by its predecessors. Provided that a project doesn't explicitly employ a feature available only in Visual Studio 2012, that project file can be opened either in Visual Studio 2010 or Visual Studio 2012. The notable exceptions to this are F# and LightSwitch projects. Once you allow Visual Studio 2012 to upgrade such projects, they can no longer be opened in Visual Studio 2010. The reason given for these exceptions is the relative novelty of F# and LightSwitch. Microsoft deemed it unlikely that a large legacy codebase existed for either, so focused less effort on preserving backward compatibility with such projects.
In addition to all the new capabilities, some welcome features in the IDE have been updated. Code snippets have been improved with the inclusion of "surround with" snippets. Whereas ordinary code snippets are pieces of skeletal code for common constructs that you simply "pour" into a single location (like a glorified paste operation), "surround with" snippets let you define an enclosing construct -- such as an if statement and its accompanying body -- that surrounds a section of selected code.
Rafts and previews
While the ability to "dock" a specific window to a particular monitor has been available in earlier versions of the IDE, Visual Studio 2012 adds a new facility (and new nautical metaphor) called a "raft." A raft is a collection of multiple windows that can be treated as a single unit for the purpose of docking.
Another welcome usability feature is the preview tab, which opens a file in a new tabbed window whenever you select a file from the solution explorer (or if you happen to step into the file in the debugger). Previously, viewing a file's content required that you explicitly open it; now you simply select it to materialize a preview window. The preview is not an editor (its content is read-only), so you must take the extra step of actually opening the file to edit it. But the preview tab is a handy feature for large projects where you need to quickly search through source files.