Thanks for the comment! You are very close. I'm actually saving both "Value" and "DisplayName" in the result. In case you are using cms.user object type and you get UserID as Value and UserName as DisplayName, you will see something like this:
If I wouldn't store the display name, I would need to somehow get the object info in order to retrieve the display name which would be shown when you open the form control and this would be more complicated as each object type uses different provider (UserInfoProvider, DocumentHelper, TreeHelper, SiteInfoProvider etc..).
Feel free to let me know if you have any further questions!