The reason Jim is an ideal writer for Spider-Man is that Harry and Spidey are so similar. In fact, Harry is snarky in the exact same way Spider-Man is in the comics. In one of the Dresden books, Harry even makes mention that he is a follower of "the Tao of Peter Parker."
OMG, a dead thread! We've gotta save it! Gimme 50 cc's of adrenaline, stat! OK, gimme those paddles... CLEAR!!!! *bzzzt*
OK, we've got a pulse. Whew, that was close.
Ahem. Yes, Harry and Spidey are similar. Jim has mentioned several times that he grew up as a big Spidey fan, so the homage Harry pays to Peter Parker is not at all surprising. It also explains why Jim jumped at the chance to write this novel, when really he was far too busy to do it.