Selina's past and origin are extremely interesting to me. Unlike most Gotham characters, her past is almost always in flux; nobody can come up with a totally definitive explanation for her skills and personality. Since most believe the end-product for the character should be a master-thief with acrobatic skills and some strength at fighting combined with a strong sense of fun and flirty behavior, there's a lot of blanks that need to be filled. Is she a kleptomaniac? Is she a self-sufficient street rat? A rejected mafia princess looking to get back at her father? A hooker with a heart of gold turned towards less degrading lines of work?
And where does she learn to fight? School of hard knocks? The armless master? Ted Grant, one of Bruce's instructors as well?
Personally, I'm hoping for some kind of Falcone connection. It technically makes her a social peer with Bruce but for a twist of fate, and gives her a reason to get more bold and audacious in her robberies. Plus, there's some suggestion that the connection is being resurrected in the comics; Falcone's returning to Gotham in the early issues of Batman: Eternal, and sometime in the storyline Selina manages to seize control of the Gotham Underworld.