The Micro Four Thirds mirrorless system is enjoying a bumper crop of native lenses, twenty five in total at the time of this writing. While a large choice of lenses may not be a big deal for casual users, it's an important factor for enthusiasts when choosing which system to invest in. In comparison, the Samsung NX system has ten native lenses in their list, the Sony NEX has seven, and the Nikon 1 has four lenses.
Besides the M.Zuiko Digital ED 12mm f/2.0, the other Micro Four Thirds prime lens Olympus introduced this year is the M.Zuiko Digital 45mm f/1.8. Where the 12mm provided a wide 24mm field of view (when you take into account Micro Four Thirds 2x crop factor), while the 45mm is a tight 90mm. It's close to the classic 85mm focal length, which is often used for portraits because the flattening of perspective at that focal length is flattering to features. Not to mention the wide f/1.8 maximum aperture, which gives you a soft, blurry background thus focusing a viewer's attention directly on your subject.
It also shouldn't hurt that Olympus' 45mm prime is a beautiful looking lens with an attractive silver finish.
The Olympus 45mm is not a big lens, it's comparable in size to the standard Olympus 14-42mm kit lens. It isn't as complicated a design as the 12mm; the manual focus ring doesn't slide back to reveal distance and depth of field indicators like the 12mm. The silver finish is metal-like, but it's not constructed out of metal, and feels a little light in the hands, not as solid as the Olympus 12mm (maybe that's why it's half the price). Still, that doesn't detract from the fact that this is an attractively-designed lens.
A Movie & Still Compatible (MSC) mechanism, similar to the 12mm, provides high-speed, near-silent auto-focus, which is especially important when shooting video, as you don't want the footage to pick up sounds from the auto-focus motor.
Micro Four Thirds lenses, when compared to other mirrorless systems like Sony NEX or traditional D/SLR camera systems, are smaller and easier to carry. With the Olympus 12mm and 45mm, plus the Panasonic Leica DG Summilux 25mm f/1.4, it's now quite possible to carry a camera and essential primes around without too much of a strain. That's quite amazing when you think about it.