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 Canon A800 and Sony NEX-3 side-by-side from the front, back and top in their relative dimensions. Canon A800 has external dimensions of 94 x 61 x 31 mm (3.7 x 2.4 x 1.22″) and weighs 186 g (0.41 lb / 6.56 oz) (including batteries). Sony NEX-3 has external dimensions of 117 x 62 x 33 mm (4.61 x 2.44 x 1.3″) and weighs 297 g (0.65 lb / 10.48 oz) (including batteries).
Below you can see the front view size comparison of Canon A800 and Sony NEX-3. Canon A800 is clearly the smaller of the two cameras. Its body is 23mm narrower, 1mm shorter and 2mm thinner than Sony NEX-3. As you can tell, actually this is not a fair size comparison since Canon A800 has a built-in lens but Sony NEX-3 doesn't. Once you put a lens on NEX-3, its thickness will increase significantly.
Now lets look at the top view comparison of Canon A800 and Sony NEX-3.
Weight is another important factor especially when deciding on a camera that you want to carry with you all day.
Canon A800 is significantly lighter (111g ) than the Sony NEX-3 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 NEX-3, the total kit will weigh much higher.
Unfortunately neither Canon PowerShot A800 nor Sony Alpha NEX-3 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
Sony NEX-3's 3" LCD screen is slightly larger than Canon A800's 2.5" screen.
In addition to the size advantage, Sony NEX-3 LCD screen also has a Tilting feature
where you can change the angle of the screen to make it easier to shoot from waist or over the head levels. On the other hand, Canon A800 has a fixed type screen which provides less flexibility in shooting positions compared to NEX-3.