Gnomes are probably the easiest race to roleplay in World of Warcraft. They have a strong (and mostly accurate) stereotype that people just get instantly, and there's a childlike "blank-slate" quality about them that means that they don't have to have complicated backstories.
In fact, you could define the gnomes as a race without a history to speak of. They are so very curious and inquisitive that they ask questions about everything, that they try to unravel any mysteries they encounter, and consider their personal life stories to be of little account. They've written tomes upon tomes on the inner workings of multi-polar data transfer relays and eletro-magnified parallel power circuits, but it never really occurred to them that they should write down the history of their species. They are a people always looking into the future, and whatever passes beyond the infinitely precious present becomes lost to them in the unseen reaches of the past -- out of sight, out of mind.
That's not to say they have no memory -- they make use of their superb memories in carefully constructing their world-renown masterpieces of technological craftsmanship! Rather, it would be better to say that their minds only serve up memories relevant to the inquiry at hand. So if the orcs paved through azeroth a while back and destroyed everything in their path, well that was bad and all but it was a long time ago and who wants to hold a grudge? If the monstrous troggs came from the bowels of the earth and destroyed their cherished technological city of Gnomeregan... well, they'd love to get it back, but it's no reason to be unkind or uncheerful!