I had a strange thing happen when first installing Visual Micro on VS2012. I am running Windows 7 and recently installed VS2012.
The steps are as follows:

1. Installed Visual Micro.
2. Opened existing and working code.ino in Arduino IDE and compiled OK.
3. Opened same code in VS 2012 as Arduino project.
4. Code failed with errors because the Arduino constant was set to 10 (I had Arduino Uno selected from the drop down.
Here is the compiler directive:

avr-g++ -c -g -Os -Wall -fno-exceptions -ffunction-sections -fdata-sections -mmcu=atmega328p -DF_CPU=16000000L -MMD -DUSB_VID=null -DUSB_PID=null -DARDUINO=10 -DVISUALMICRO_COMPILER_VER=1 

As you can see the Aduino constant was being set to 10 instead of 101.

I tried several things and cold not get the constant to the correct value. I finally changed the version.txt in the Arduino/lib directory from 1.0.1 to 100 and everything started working OK. After compiling and testing OK, I changed the version.txt back to 1.0.1 and it works OK now.

The setting now shows up as:

avr-g++ -c -g -Os -Wall -fno-exceptions -ffunction-sections -fdata-sections -mmcu=atmega328p -DF_CPU=16000000L -MMD -DUSB_VID=null -DUSB_PID=null -DARDUINO=100 -DVISUALMICRO_COMPILER_VER=1 


Not sure what happened, but just in case this happens to someone else.