I have been laboring through setting up Custom Attributes and automatic validators in C#.NET.  It's very cool stuff, and as explained to me by my far more experienced lead, going to make our downstream efforts vastly simplified.

I was bashing at the keyboard aimlessly over this when I happened upon this article:  
   Attributed Programming in .NET Using C#
which has really helped me a great deal.  If you are interested in building custom attributes for business object entity classes, and you should be, check it out.