So I pressed something and now I can't see my dwarves. Is there a hot-key that centers my screen on my dwarves?
To view any particular dwarf use the units screen, select the dwarf you want and do a creature zoom.
You can also setup hotkeys for a location with the hotkey screen. On the hotkey screen, press the appropriate function key (F1,F2, etc) and then press z to set the location to zoom to. You can optionally press n to name the location, which I find very useful.