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 FujiFilm S2800HD and Panasonic GX1 side-by-side from the front, back and top in their relative dimensions. FujiFilm S2800HD has external dimensions of 110 x 74 x 82 mm (4.33 x 2.91 x 3.23″) and weighs 437 g (0.96 lb / 15.41 oz) (including batteries). Panasonic GX1 has external dimensions of 116 x 68 x 39 mm (4.57 x 2.68 x 1.54″) and weighs 318 g (0.70 lb / 11.22 oz) (including batteries).
Below you can see the front view size comparison of FujiFilm S2800HD and Panasonic GX1. Panasonic GX1 is 6mm shorter and 43mm thinner than FujiFilm S2800HD but it is also 6mm wider. As you can tell, actually this is not a fair size comparison since FujiFilm S2800HD has a built-in lens but Panasonic GX1 doesn't. Once you put a lens on GX1, its thickness will increase significantly.
Here is the back view size comparison of FujiFilm S2800HD and Panasonic GX1.
Weight is another important factor especially when deciding on a camera that you want to carry with you all day.
Panasonic GX1 is significantly lighter (119g ) than the FujiFilm S2800HD 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 GX1, the total kit will weigh much higher.
Unfortunately neither FujiFilm FinePix S2800HD (FinePix S2900HD) nor Panasonic Lumix DMC-GX1 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 Bridge Cameras with Weather Sealing Top Mirrorless Cameras with Weather Sealing
LCD Screen Size and Features
FujiFilm S2800HD and Panasonic GX1's LCD screens has the same diagonal size of 3".
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.