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 Nikon D5100 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). Nikon D5100 has external dimensions of 128 x 97 x 79 mm (5.04 x 3.82 x 3.11″) and weighs 560 g (1.23 lb / 19.75 oz) (including batteries).
Below you can see the front view size comparison of FujiFilm S2800HD and Nikon D5100. FujiFilm S2800HD is 18mm narrower and 23mm shorter than Nikon D5100 but it is also 3mm thicker. As you can tell, actually this is not a fair size comparison since FujiFilm S2800HD has a built-in lens but Nikon D5100 doesn't. Once you put a lens on D5100, its thickness will increase significantly.
Here is the back view size comparison of FujiFilm S2800HD and Nikon D5100.
Weight is another important factor especially when deciding on a camera that you want to carry with you all day.
FujiFilm S2800HD is significantly lighter (123g ) than the Nikon D5100 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 D5100, the total kit will weigh much higher.
Unfortunately neither FujiFilm FinePix S2800HD (FinePix S2900HD) nor Nikon D5100 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 DSLR Cameras with Weather Sealing
LCD Screen Size and Features
FujiFilm S2800HD and Nikon D5100's LCD screens has the same diagonal size of 3".
On the other hand, Nikon D5100 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. FujiFilm S2800HD's LCD screen is a fixed type which provides almost no flexibility in shooting positions compared to D5100.