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 Panasonic ZS3 and Olympus E-PL1 side-by-side from the front, back and top in their relative dimensions. Panasonic ZS3 has external dimensions of 103 x 60 x 33 mm (4.06 x 2.36 x 1.3″) and weighs 229 g (0.50 lb / 8.08 oz) (including batteries). Olympus E-PL1 has external dimensions of 115 x 72 x 42 mm (4.53 x 2.83 x 1.65″) and weighs 334 g (0.74 lb / 11.78 oz) (including batteries).
Below you can see the front view size comparison of Panasonic ZS3 and Olympus E-PL1. Panasonic ZS3 is clearly the smaller of the two cameras. Its body is 12mm narrower, 12mm shorter and 9mm thinner than Olympus E-PL1. As you can tell, actually this is not a fair size comparison since Panasonic ZS3 has a built-in lens but Olympus E-PL1 doesn't. Once you put a lens on E-PL1, 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.
Panasonic ZS3 is significantly lighter (105g ) than the Olympus E-PL1 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-PL1, the total kit will weigh much higher.
Unfortunately neither Panasonic Lumix DMC-ZS3 (Lumix DMC-TZ7) nor Olympus PEN E-PL1 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
Panasonic ZS3's 3" LCD screen is slightly larger than Olympus E-PL1's 2.7" screen.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.