You can easily improve the buttons by adding 1-2 layers of electrical tape to the switches inside.

In addition to this simple step you can take it a bit further and completely fix the side buttons as well as mouse 1 and 2.

Side Buttons:
Remove the side buttons from the mouse and bend the plastic springs (two curved arms on the inside of the side buttons) further. For some reason the mouse comes with the plastic springs not bent far enough, resulting in a collapsed feel. You have to be careful here because the plastic springs are delicate and bending them too far will weaken them greatly. Instead of bending the springs too much you will want to wrap one or two pieces of electrical tape around the tips of the springs where they make contact with the inside of the mouse. This will add extra resistance without bending the arms any further. Finally tape the two buttons together on the inside right above where the springs protrude from them, 1-2 layers of electrical tape will add some extra durability, holding the buttons in place and taking some of the pressure off the plastic springs. It will also help keep the buttons flush with each other and the outside of the mouse when you reassemble it.

Mouse 1 and Mouse 2
Completely disassemble the top portion of the mouse. Here you will see once again Microsoft has used plastic springs which collapse over time. Their own weight will eventually be enough to keep the buttons down. You can fix this by taping a bit of plastic/card stock underneath the buttons' springs to prop them up. A little bit goes a long way here, if you prop them up too high the buttons will not easily make contact with the switches, forcing you to press them harder and causing quick degredation of the plastic springs.

If you have the original ms3.0 and the latest ms3.0, switching the mouse wheel from the old one into the new one will improve the mouse wheel. I discovered a couple weeks ago that the plastic on the axle of the old wheel was thicker than the new one, resulting in a tighter fit when placed into the more recent ms3.0.

If you aren't fortunate enough to own both, you can add electrical tape to the piece of curved plastic that holds the axle in place. This will give you a snug fit and some more resistance while turning the wheel. You may have to do this even if you are lucky enough to have the original ms3.0 wheel in hand, it seems after a couple weeks the extra friction that I achieved by replacing the wheel with the old one has subsided some. I will probably combine both methods, or maybe not I don't use the mouse wheel in game.

My original ms3.0 cable went out prior to the latest release of the ms3.0. Luckily the usb cables are replaceable. In my original mouse I opted to use an intellimouse 1.1 cable as a replacement. In my current ms3.0 I switched cables with my death adder. The smaller and thinner cable prevents me from having to use a mouse cord weight, before with the longer thicker cable my 3.0 cable would continuously fall off the desk due to it's own weight. Preferably I would like to have a cloth covered cable such as the one found on some logitech mice, I do not know if those are removable but if someone has one it's worth a try. I'll just add that these cables are really tightly fit into their female counterpart on the board of the mouse. It's best if you complete remove the board so you can use one hand to hold the female end against the board, this will prevent you from ripping it off/causing it damage. If you have a small flat head screw driver, you can probably pry the two ends apart easier than you can pull them apart.