I've got this one and really like it. One of the big differences between the two is sensor size. Nikon ILC's have a 1" sensor. Panasonic and Olympus make micro 4/3 cameras (4/3" sensor).
Panasonic and Olympus lenses are interchangeable since they are both m4/3 (though Panasonic uses lense stabilization while Olympus uses body stabilization, IIRC). You can buy other lenses for any of these systems and use an adapter but you won't be able to use things like auto-focus and power zoom on them.