There have been lots of improvements, beginning, I suppose, with the introduction of rifling. Then they progressed through various ignition systems, case designs and powder compositions. There is also a vast array of warheads available for the projectiles themselves.
Both, yes. Lasers are often mounted on guns for sighting purposes (as seen in the movies) and are currently being fitted to airplanes for shooting down missiles. There won't be laser rifles anytime soon, though (too big).
THe only and not so recent physical improvement I can think of for guns (and metalstorm seems to be a vast improvment over this even) was getting rapid fire gatling guns by using an electric spark as a hammer onto the primeror to ignite the powder instead of a physical firing pin. I believe that's how some of the guns on our jets are fired.
I heard of these electric guns. If they had them in rifles and hanguns perhaps Id use one for range fun but I would never trust my life to it. I would imagine they keep the same mechanism due to the fact that it works really well and what is at stake if they screw up. I spoke with some engineering folks who figured out creative ways to improve powder performance, they claim the Army wasnt all that interested.