One of my favourite features of the Fuji x100s is it's leaf shutter. A leaf shutter allows for extremely high speed sync with a flash. When using flash a traditional DSLR is usually limited to a shutter speed of below 1/250sec. The leaf shutter on the x100s allows for flash sync at speeds in excess of 1/1000sec.
While this might not sound like much, when you combine this with the x100s's built in 3 stop Neutral Density filter, all of a sudden you have a compact camera that can overpower the sun with a small handheld flash unit while still allowing you to shoot at a shallow depth of field.
The shot below of Shelley was taken in middle of the day when the sun was at it's brightest. My camera settings were 1/1000sec, ISO 200, f4.0 with the ND filter on.
I lit the scene with a handheld LumoPro LP180 flash, trigged with 2 x pocket wizard x's, at full power shot through a Metz 40-40 pop up soft box.
The softbox is small enough for me to be able to hold in one hand and shoot my x100s with the other. The compact size makes it perfect for travel portraits.
The Metz 40-40 is a really well built, quick to assemble, portable softbox. The flash unit attaches via a plastic bracket on the rear of the softbox. This bracket is probably the weakest part of the unit and I fear over time may give way, particularly when using the softbox handheld on location.
When used in close to the subject the Metz 40-40 gives a very flattering soft light that can be controlled much more than when working with an umbrella. It's ideal for single subject portraits and small enough to travel easily with. For group portraits or wider, full length shots, I'd look at using an umbrella instead.