Obviously, tearing them down every time it kicks is a great habit. However, I tear them apart about every two batches. I usually just do a good rinse and then fill about halfway with a pbw or oxy clean solution, let that set a few minutes, pressurize the keg and run the solution through the lines. Empty cleaning solution and repeat the above with star san. I store my "empty" kegs in a pressurized star san solution.
No problems with infections or any off flavors. If the beer is good in the keg when it kicks, it begs the question, "Why do you have to clean it to begin with?" But seriously, cleanliness is the most important thing.