Joaogl: I made a basic physics engine for a (2D) Asteroid type of game with bouncing asteroids and a tractor beam. It was so rewarding to when I saw even simple polygons behave like "real" objects. A childlike bliss!
Gamerulf: Yes, movement is part of physics but it can be more or less "real". That is, if you want stuff to behave more like in the real world a simple "x++" won´t suffice. You´ll have to start to calculate how forces affects objects, how objects react in a collision and so on. I really recommend the links below. They are a good read if you have the time. Wildbunny and Chris Heckers articles taught me a lot.
And using 2D physics in a 3D world isn´t such a good idea since you have no depth. But even so, I think it´s a good idea to start out 2d just to get a grip of the concepts. When you get to the point that you need to solve collisions between multiple objects it´s pretty nice not to be bothered by that extra dimension I guess...