By popular request...
Guidelines are visible column indicators for the VS Editor. For more info on how to enable them, check out http://blogs.msdn.com/saraford/archive/2004/11/15/257953.aspx
Note: I've spent lots of cycles testing these on Visual Studio 2005 Beta. I've done very limited tested on Visual Studio .NET 2003 and haven't done any testing with these on Visual Studio .NET 2002. I can't ensure product stability for these versions, so use at own risk.
If you encounter an issue or have suggestions or ideas about how we can make guidelines better, let me know!