I'm not sure if this is the best-practice, but was a hard to discover methodology for cycling through a documents properties.  Hope this speeds up development for someone in the future.

 
 MyDataType mydata = new MyDataType();
 
 doc = new Document(Convert.ToInt32(Request.QueryString["nodeID"]));
 //the node ID can be gotten by several methods, we were passing by query string

 foreach (umbraco.cms.businesslogic.property.Property prop in doc.GenericProperties)
 {
   //Do something

   //To work on a specific type of property type by GUID
   if (prop.PropertyType.DataTypeDefinition.DataType.Id == myData.Id)
   {

   }
 }

Again there may be a better way, but the documentation I scrapped together on the Document Class and Property Class are not much help for specific class properties and methods.

Visual Studio hinted that doc.GetProperties was deprecated, but didn't lead me to doc.GenericProperties explicitly.

Stay classy Umbraco.