While you were gone
Since the launch of VS2012, Microsoft has released four updates referred to as 2012.1, 2012.2, and so on. Each have added functionality to the original program, and each installed package is cumulative, meaning that only the newest one has to be installed to provide the benefits of all previous updates.
VS2012 Update 1
First and foremost is the ability VS2012.1 provides for C++ developers to target Windows XP clients while using the VS2012 compiler. This is a key ability if you desire to continue compiling applications that run on Windows XP and Vista as well as Windows 7 and 8. JavaScript programmers will appreciate the inclusion of memory profiling and memory analysis tools. SharePoint developers will gain load testing support and the use of SharePoint emulators. Full details are available at http://support.microsoft.com/kb/2797915.
VS2012 Update 2
This update includes ASP.NET and Web Tools 2012.2, unit testing support for Windows Phone, and broader unit testing capabilities for Windows Store apps. 2012.2 includes a host of bug fixes and stability improvements that benefit all areas of the program, right from the debugger to memory leaks in C++ based solutions, and several use cases that would cause the IDE to crash. Full details are available at http://support.microsoft.com/kb/2797912.
VS2012 Update 3
2012.3 primarily provides bug patches and performance improvements. Notable for those using VS2012 and VS2013 concurrently is 2012.3's improved compatibility with VS2013 projects. Several stability fixes were made that among other things prevent crashes in web projects, fix a conflict between VS2012 and VS2010, and correct slowdowns when developing mixed-mode C++ applications. Installing Update 3 provides the ability to install the Microsoft Visual Studio Tools for Git, a popular open source version control system. Full details are available at http://support.microsoft.com/kb/2835600.
VS2012 Update 4
Similar to 2012.3, this update is focused in bug fixes and stability enhancements. As this release coincides with the production release of VS2013, it provides some improved compatibility for sharing projects/solutions between VS2012 and VS2013. Full details are available at http://support.microsoft.com/kb/2872520.
Tip
At the time of this writing, there is no reason to avoid installing the latest update available for VS2012 whether using an Express edition or one of the premium editions. Several meaningful improvements have been made to the product since its original release date that benefit all users. Microsoft provides both a web-based installer and a complete standalone ISO at http://go.microsoft.com/fwlink/?LinkId=301713.