As corrupting? Well sure, if for the sake of this argument I started drawing from real life, on which the Dresden Files is a commentary as much as it is a fantastic story then I would have ample evidence. In the setting from what we've been given? One example comes to mind, but you would probably dismiss it out of hand since it relates back to what I was saying about fantastic racism.
The example would be Harry's changing attitude towards ghouls. At first he's complacent as much as one can be about cannibals because that's just their nature. When he's exposed to something that changes that attitude he changed gears to indiscriminate hate. He uses magic viciously, the use of magic reinforces his hatred and he begins changing to react like that with his magic to all ghouls.
Actually, another example just came to me. There's also his case history overall, for instance when Marcone mentions that he'll take the bet that Harry destroys their mutual enemy. Harry ends up musing on that, more often than not his enemies end up dead; this would be because he has grown accustomed to using his magic to kill his enemies either directly or indirectly.
