In an attempt to do the character some justice, I must first say that no matter how clumsy Haruto is, he's not what we'd call "stupid". Sure, he has his moments, but he's new, so you'd have to give him a bit of leniency.
Upon Robin's arrival, Sakaki becomes worried of what might lead to his replacement; her hunting skills obviously surpass his. However, he was not quick to judge her, and easily warms up to her. Although he may be ambitious about his career, he holds nothing against Robin; one could say he admires her in the slightest bit, if anything else.
Sakaki somehow manages to loose his calm collective that he carries everywhere else when running headfirst into danger, almost throwing away his life. I think he tries his best at herioc deeds, and it looks like he does, in fact, take his work seriously. Unfortunately, for Sakaki is so well known for his blunders and mess-ups at headquarters. Though he does get the usual lecture from Kosaka from time to time, but he has, so far, done nothing serious. Why he was never fired given the situations-- we may never know. There's a possibility that STN-J may be using him, or they probably need all the working bodies they can get. That isn't to say he isn't without some sort of talent; he seems to have an above average control of firearms. He also seems to have a slight temper, becoming easily annoyed when his authorities push him around.
On the question of any kind of "special abilities" he has, the series makes a statement that no human is without a drop of witch blood. Theoritically, every person has a witch somewhere in their ancestry, no matter how small it is. The witch being hunted during episode 3, Dancing in Darkness, has an ability to make himself younger by sucking the life out of another witch, a seed, or a decendent of one. As solid clue as to Haruto's heritage is when that witch attempt to suck the life force out of him. Of course, no assuptions are being made here since he rarely shows any kind of abnormal ability, if any at all.
He's also a fairly independent character, which sometimes has its ups and downs. He doesn't usually request for help, but receives it from time to time, usually in the form of assistance from Amon.
Er, other than that, he seems to enjoy riding his motorcycle as a means of transportation. He tends to use it often in hunts, and is probably somewhat fond of it.