Stuff-Review has made a nice little chart that pits the newcomer against the almost established crowd. That's all pretty theoretical though, since 3 of the 4 cameras are practically not available in the majority of the western world:
"Despite coming late to the party, Fujifilm intends to enter with a bang. The X-Pro1 has Leica-like controls with individual shutter speed and exposure compensation dials, while each lens has a manual aperture ring. Fujifilm has also improved on the X100′s hybrid electronic/optical viewfinder, and the second generation has found its way in the X-Pro1.
Before we go on to the main dish, here's a reader commentary on the same Engadget page:
"Why does everyone simply forget panasonic G3? It has the same sensor as GX1, marginally bigger body but with EVF builtin, an extremely handy tilted screen with touch focus and same resolution as gx1. It's basically the same or even better than GX1!!
Dials! Dials everywhere, OM-D=Oh My Dials? Olympus really means business with this one. No fancy designer needed here, just the best example of retrography this editor has ever seen, and yes, i include all the recent Fujifilms, and the Panasonic GX1.
No longer the stuff of rumors, here's the E-M5 straight from the horse's mouth: