It would be really great to make error messages relating to a property on the property page refer to the label on the page and not the property's VB Designer name. Quite often a property's VBDesigner name won't match the label on the property pages.
For example, for the property "Custom.SomePropertyName", if I use a regex for input restriction and the user's input fails the check, the error message is:

"The value you entered is not valid for the property 'SomePropertyName'.
You entered an incorrect value."

Instead, the error should refer to the label on the property page, which might be "Useful Property":

"The value you entered is not valid for the property 'Useful Property'.
You entered an incorrect value."

Given that the user sees the label on the property page and is completely ignorant of the internal name, display name, VBScript name, and VB Designer name, the label should always be referred to in error messages.