When I moved to North Carolina not long ago, I was excited to register to vote. I registered as an Unaffiliated voter. This way of registering allows me one huge advantage. I can choose which party to vote for on primary day. In the upcoming presidential election, I will choose to vote in the Republican primary if the nominee hasn't been chosen by then.
I also registered as unaffiliated because in North Carolina, anyone can look up my voter registration, and I didn't want any future employers choosing not to hire me based on my registration. I know that sounds silly, but I am sure it happens. It works for me.
While I identify with the Democrats most often, I vote for person over party. Now, being completely honest, I haven't voted for a Republican since I voted for GWB in 2000. Yes, it was a mistake. I'm just glad I realized that by 2002 and voted straight Dem since then.
One other reason I don't register as a Democrat is because I don't like having my vote taken for granted. I've found that being registered Unaffiliated means candidates will work harder for my vote.
Anyway, I just thought I'd share a little since others have talked about why they are registered the way they are.