I've got one and the only thing I did was clean the contacts under the speedo head this spring. One thing you may have to do if you notice it turning off a lot and having big jumps in speed is slightly heat and bend the little locking tab up, that helped mine out a lot.
I run the original plug, only replaced the plug wire because the boot broke after I'd installed the speedo, I don't have the pickup wire running that terribly far from the coil and it's always worked great.
A little trick my buddy showed me on setting one. Use the actual wheel diameter chart in the instructions, put a dot of 3&1 oil on your tire, roll the bike forward (with your weight on the bike) until the dot hits the ground twice, measure between the dots, use the formula in the instructions and you'll have the true tire diameter.