Don't be in any doubt: this is a big camera. It's not clear whether this is because FujiFilm believes a camera needs to be a certain size in order to be comfortable and usable, or because the sensor isn't the limiting factor when it comes to miniaturization. The advantage is that you have plenty of space on the body for all of those switches and buttons.
In your hand
The advantage of the S100FS's size is that there's plenty of it to grab hold of. For a camera that is around the same size as a small DSLR, it's got a remarkably good grip. Not only does it feel comfortable in the hand but the buttons are generally well placed and within easy reach, even when you've got your eye up to the electronic viewfinder.
There's a tilting screen at the back that can be adjusted for overhead, waist-level or tripod-based shooting. It means the screen isn't as big as it could otherwise have been but it's pretty useful. And, because the S100FS is has been designed exclusively to be used via electronic viewing, its use is generally faster and more consistent than in DSLRs with 'Live view.' There's even a remote shutter release cable available, for those users wanting to use the S100FS on a tripod.
The electronic viewfinder has a high-resolution, 200,000 pixel display that sequentially displays red, green then blue at each position. The advantage is high resolution and, in theory, color accuracy. The only disadvantage is that if you move the camera too quickly, the different colors get out of sync. (The glitchy results are a bit like running 'round, wearing red and green 3D glasses whilst drunk.)
The most obvious thing you notice on the S100FS, once you've got over how many external buttons its got, is just how big the mode dial is. It's a huge, turret-like thing full of customizable settings and such like. This includes the entertainingly-named 'FSB' mode which entails 'Film Simulation Bracketing,' rather than a spy-camera mode.
The S100FS offers more than simply DSLR-like styling: it also offers a greater degree of external control than most entry-level DSLRs. On the right-hand shoulder, there's a control wheel which, when used with the fairly well-positioned exposure compensation button, gives a manual mode that behaves just like it would on an entry-level DSLR. The dedicated ISO button is also a plus.
Here's something you don't usually see on anything below a mid-range DSLR: a metering mode switch. You can choose between spot, pattern (multi-zone), or average metering. This dictates what information the camera uses to set the exposure, or what information it provides to help you manually select the exposure. There's also an exposure-lock button.
Another common DSLR feature is the AF mode selector. This gives direct control of whether the camera continuously adjusts focus, makes just one attempt or leaves you to focus manually, using the focus ring on the left. The central button engages autofocus in manual mode, allowing you to jump into focus and fine-tune. There's a button for changing shooting mode and one for turning anti-shake on an off on the flank too.
Four-way controller? It's got one of those as well. Pressing the magnifying glass button in record mode engages digital zoom, which is particularly useful for manual focusing. In playback mode, the up and down arrows zoom in and out, only allowing navigation around the screen once the left or right buttons have been pressed.
The S100FS also has a hotshoe for an external flash, though FujiFilm doesn't have its own through-the-lens (TTL), metering system for external flashes, so it's just a traditional, generic type.
There's also a PC sync socket for connecting other off-board flashes. This is a really unusual feature and, again, isn't common below mid-price DSLR level.
Unlike the S9000 and S9100 (S9500 and S9600 for those in Europe or Asia), the S100FS takes SD or SDHC cards, rather than Compact Flash. It continues to offer support for xD, but we wouldn't recommend using them unless you already own several.
FujiFilm has also moved away from using AA batteries, opting instead for a rechargeable Lithium Ion block. This makes the camera lighter, but sees the battery life drop to 250 shots (Compared to the S9100's 320 with NiMH AA cells). The larger screen and image stabilization won't have helped this figure. The new battery puts out 7.2V - more than the combined output of four AAs (4.8-6V), which may explain the change.
FujiFilm has bestowed the usual selection of ports on the F100FS - power input, A/V out and a mini USB socket for connecting the camera to a computer. However, the USB port can also be used to connect and optional remote trigger, another nice feature for people making regular use of tripods.