In Uruguay pizza is not round, and slices are not triangular, well now is getting more common, but when I was a kid, round pizzas could only be seen in movies.
I guess the reason lies in the traditional usage of a spade (pala, is spade the right word? is more like a paddle) in the cooking process. Pizza here is prepared a la pala, using a sort of spade to put the pizza into, and take it out from the oven, typically a firewood oven. The pizza is given a rectangular, long and thin shape, to be better handled with the spade. In some places pizza is sold by the meter.
Also in Uruguay, if you order a pizza, you'll get one without any mozzarella. If you want the portion with mozzarella, you have to order a mozzarella :D Informally called "muzza".
It is also usually ordered along with a traditional dish in Uruguay named Fainá (farinata in italian), which is a sort of thin bread mixed with cheese (depending on the receipe), and served with pepper. It's typical to order it from the border (faina de la orilla), which is kind of stupid, taking into account I've never met anyone that likes it from the middle (everybody orders it "de la orilla"). If you ask me among the best places to have Pizza in Uruguay is a bar called Costa Azul by the Rambla de Pocitos. One portion of pizza costs around 20 pesos, almost 1 usd, and one portion of muzza costs two times that amount.
Pizza is usually delivered wrapped in paper and nylon to separate the layers of pizza, muzza, faina, etc. The paper is typically used to get your hands cleaned.
The size of the portion also changes from bar to bar, and it depends heavily on the cookers mood when cutting the portion. One interesting experiment I like to make is to order one portion, and after a while order two portions. Usually two portions aren't two times one, but more like 1.5, and if you order three you'll get whatever, since it's eyed measured. When you are uruguayan, young, penniless, and starving this is the type of useless things that you pay attention to.
It is typical to have a slice of muzza, with a slice of faina on top, and this is called pizza a caballo (pizza on horseback?).