I have worked for customers that have set limitations on the number of characters that a line may contain. Unless you are really paying attention to the lower right hand corner of Visual Studio, especially if you have a high resolution screen, it is not easy to adhere to the limitations. Here is a little Visual Studio trick that I came across that will show visual cues in the form of a line at specified positions. This registry hack works for both Visual Studio 2003 and Visual Studio 2005.
 

For Visual Studio 2003:
[HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\7.1\Text Editor]
"Guides"="RGB(128,0,0) 80, 120"


For Visual Studio 2005:
[HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\8.0\Text Editor]
"Guides"="RGB(128,0,0) 80, 120"
 

In this case guidelines are shown at 80 and 120 characters respectively.

Enjoy…