Size and weight is a big decision factor when you are trying to find the ideal camera for your needs.
In this section, We are going to illustrate Nikon S9100 and Olympus E-PM2 side-by-side from the front, back and top in their relative dimensions. Nikon S9100 has external dimensions of 105 x 62 x 35 mm (4.13 x 2.44 x 1.38″) and weighs 214 g (0.47 lb / 7.55 oz) (including batteries). Olympus E-PM2 has external dimensions of 110 x 64 x 34 mm (4.33 x 2.52 x 1.34″) and weighs 269 g (0.59 lb / 9.49 oz) (including batteries).
Below you can see the front view size comparison of Nikon S9100 and Olympus E-PM2. Nikon S9100 is 5mm narrower and 2mm shorter than Olympus E-PM2 but it is also 1mm thicker. As you can tell, actually this is not a fair size comparison since Nikon S9100 has a built-in lens but Olympus E-PM2 doesn't. Once you put a lens on E-PM2, its thickness will increase significantly.
Comparison image of Nikon S9100 and Olympus E-PM2 Size, Weight and External Dimensions - Front View
Now lets look at the top view comparison of Nikon S9100 and Olympus E-PM2.
Top View Comparison image of Nikon S9100 and Olympus E-PM2 Size
Weight is another important factor especially when deciding on a camera that you want to carry with you all day.
Nikon S9100 is significantly lighter (55g ) than the Olympus E-PM2 which may become a big advantage especially on long walking trips.
Again, this comparison may not be very useful in real life as we are comparing the weight of a camera with a built-in lens to the body-only weight of an interchangeable lens camera. Once you put a lens on E-PM2, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither Nikon Coolpix S9100 nor Olympus PEN E-PM2 provides any type of weather sealing in their body, so you have to give extra care especially when you are shooting outdoors. If weather sealing is a must-have feature for you, check these sections: Top Compact Cameras with Weather Sealing Top Mirrorless Cameras with Weather Sealing
LCD Screen Size and Features
Nikon S9100 and Olympus E-PM2's LCD screens has the same diagonal size of 3".
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.