>That pi**es me off outright ...
>When I see things named like reserved words and thus turning blue in my code window, I normally turn red :0)
>
>How harmful it can really be actually doing it ? Are you aware/heard of real damages caused by this mishap ?

The damage is to your nerves. You either run into a very interesting debugging session (or night ;) or you are annoyed by having to type the alias each time you use the field. Then you realize that with Code References you could have renamed the field six times already and tracked it down the whole app.