Size and weight are big decision factors when you are trying to find the ideal camera for your needs.
In this section, we are going to illustrate the Sony T900 and Olympus E-PM2 side-by-side from the front, back and top in their relative dimensions. Sony T900 has external dimensions of 98 x 58 x 16 mm (3.86 x 2.28 x 0.63″) and weighs 143 g (0.32 lb / 5.04 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 the Sony T900 and the Olympus E-PM2. Sony T900 is clearly the smaller of the two cameras. Its body is 12mm narrower, 6mm shorter and 18mm thinner than Olympus E-PM2. As you can tell, actually this is not a fair size comparison since Sony T900 has a built-in lens but Olympus E-PM2 doesn't. Once you put a lens on E-PM2, its thickness will increase significantly.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Sony T900 is significantly lighter (126g ) 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 the Sony Cyber-shot DSC-T900 nor Olympus PEN E-PM2 provides any type of weather sealing in their bodies, 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
Sony T900's 3.50" LCD screen is slightly larger than Olympus E-PM2's 3" screen.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.