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-620 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-620 has external dimensions of 130 x 94 x 60 mm (5.12 x 3.7 x 2.36″) and weighs 500 g (1.10 lb / 17.64 oz) (including batteries).
Below you can see the front view size comparison of Panasonic ZS3 and Olympus E-620. Panasonic ZS3 is clearly the smaller of the two cameras. Its body is 27mm narrower, 34mm shorter and 27mm thinner than Olympus E-620. As you can tell, actually this is not a fair size comparison since Panasonic ZS3 has a built-in lens but Olympus E-620 doesn't. Once you put a lens on E-620, its thickness will increase significantly.
Here is the back view size comparison of Panasonic ZS3 and Olympus E-620.
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 (271g ) than the Olympus E-620 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-620, the total kit will weigh much higher.
Unfortunately neither Panasonic Lumix DMC-ZS3 (Lumix DMC-TZ7) nor Olympus E-620 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 DSLR Cameras with Weather Sealing
LCD Screen Size and Features
Panasonic ZS3's 3" LCD screen is slightly larger than Olympus E-620's 2.7" screen.
On the other hand, Olympus E-620 sports a Fully Articulated screen
which you can change the angle and position of the screen almost freely, making it possible to shoot from waist or over the head levels, and especially very useful for shooting selfies and video. On the other hand, Panasonic ZS3 has a fixed type screen which provides almost no flexibility in shooting positions compared to E-620.