In Lazarus you can see it by hovering mouse over the type name, and it will tell what unit it comes from. Or you can ctrl-click the type and it will take to definition. I think same thing applies for Delphi.
Edit: Nice dj, covering same things at the same time
I prefer not to use prefixes for class names, but unit names yes. Not any long ones because we're going to be adding them to uses list, and for convenience sake short is better.
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