>In some of our code, we have carry out certain bits of code based on a property value (eg. in our error logging routine, I log different information based on the value of a property in our error object). There are only a small set of valid values for this property and so I've #define'd the values in our header file.

The problem is that constant values don't exist at design time, so you can't use the property sheet to assign a constant value to a property. If you need to do this, put code in the object's init to set the property to the value of the constant.