Mainly we still use Visual Studio 6 (C and VB), sometimes I use 2008 because it is far more comfortable but the troubles of bringing back the code and the solution under VS6 for my colleague is a good deterrent.
Luckily it is extremely fast to boot, while 2008 is sluggish at best (we have cheap old workstations).
And most: more modern compiler and linker leads to smaller and faster code
I know, I benchmarked VS6, 2008 and 2012 on several computational heavy routines and proved that.
Still, our interface is VB6, our codebase is VC++6 with DSW and DSP files which must be mantained and most of all, my senior colleague and supervisor resist to the "upgrade" to VS2008 as stubbornly as a donkey
I'd like to move to 2008, maybe with a decent PC for a change, but it will be rough. It's highly probable we'll change directly to 2012 for the next interface, which will be WPF, but right now we're drowning in emergencies and can't make any progress in the improvement of the software.
It's pretty solid and I did not find anything that does not work as smooth as in VS 2013 [at least for the things I am interested in]. For me that is fully sufficient + I can use Roslyn without much trouble.