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 S950 and Olympus E-P1 side-by-side from the front, back and top in their relative dimensions. Sony S950 has external dimensions of 93 x 56 x 24 mm (3.66 x 2.2 x 0.94″) and weighs 167 g (0.37 lb / 5.89 oz) (including batteries). Olympus E-P1 has external dimensions of 121 x 70 x 36 mm (4.76 x 2.76 x 1.42″) and weighs 355 g (0.78 lb / 12.52 oz) (including batteries).
Below you can see the front-view size comparison of the Sony S950 and the Olympus E-P1. Sony S950 is clearly the smaller of the two cameras. Its body is 28mm narrower, 14mm shorter and 12mm thinner than Olympus E-P1. As you can tell, actually this is not a fair size comparison since Sony S950 has a built-in lens but Olympus E-P1 doesn't. Once you put a lens on E-P1, its thickness will increase significantly.
Here is the back view size comparison of the Sony S950 and Olympus E-P1.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Sony S950 is significantly lighter (188g ) than the Olympus E-P1 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-P1, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither the Sony Cyber-shot DSC-S950 nor Olympus PEN E-P1 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
Olympus E-P1's 3.00" LCD screen is slightly larger than Sony S950's 2.7 screen.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.