Size and weight are big decision factors when you are trying to find the ideal camera for your needs.
In this section, we are going to illustrate the Sony T99 and Nikon D90 side-by-side from the front, back and top in their relative dimensions. Sony T99 has external dimensions of 93 x 56 x 17 mm (3.66 x 2.2 x 0.67″) and weighs 121 g (0.27 lb / 4.27 oz) (including batteries). Nikon D90 has external dimensions of 132 x 103 x 77 mm (5.2 x 4.06 x 3.03″) and weighs 703 g (1.55 lb / 24.80 oz) (including batteries).
Below you can see the front-view size comparison of the Sony T99 and the Nikon D90. Sony T99 is clearly the smaller of the two cameras. Its body is 39mm narrower, 47mm shorter and 60mm thinner than Nikon D90. As you can tell, actually this is not a fair size comparison since Sony T99 has a built-in lens but Nikon D90 doesn't. Once you put a lens on D90, 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.
Sony T99 is significantly lighter (582g ) than the Nikon D90 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 D90, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither the Sony Cyber-shot DSC-T99 nor Nikon D90 provides any type of weather sealing in their bodies, 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
Sony T99 and Nikon D90's LCD screens have the same diagonal size of 3.00 inches.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.