Snape will finally be on the good side.

Although he has been on the side of good before, such as in book 1 and 2. And, well, just generally. As D'Archangel, I believe, has said, Snape is lawful unpleasant.

While he is often annoying; he has consistently worked for good, except for book 6 being open to interpretation. Obviously, he does have a past of doing the wrong thing, but that was a long time ago.

Snape is on the good side even now.

I still think his being good is a big ruse. He could easily be a death eater spy.

It' clear that Snape has been a double-agent for some time. He's a good guy, but we only find that out after he's dead (or as he's dying)

SPOILERS for the Half-blood Prince follow:

Snape IS on the good side. Big D knew he was going to die (and be reborn ... remember the phoenix) and tried to make of point of that. He persuaded Snape to kill him in order to get that reputation into those deatheaters heads.

I think that in the end of all things he's only out for himself and what he can get out of a situation. Being percieved as being a double agent was the best option for HIM in the series, and if he really needs to choose a side in the end it'll just be what's in his best interests to do.
But, the world isn't divided into good people and death eaters.

Olav and Mike clearly understand Jo Rawlings well.

I love him. He's the best character in the books in my opinion. I always thought he was good.