Is Dublin dangerous?

Within an hour of arriving in Dublin I was warned by my cab driver, and a complete stranger on the street, to not wander around or I'd be mugged. I'm staying by Christ Church and understand there's a methadone clinic near by. I'm from Chicago so I'm used to vagrants, but dual warnings by strangers has kind of rattled me.

Edit: Thanks for all the advice guys! I went out last night and had a blast. I think I was overly paranoid.