I had an '03 that I never adjusted the for more than 3 years and nearly 300 hours. I did, however, check them 5 or 6 times over that period. My '06 has gone well over that, and had a top end replaced, but only one valve replaced, and two others adjusted. If you find them in spec, no need to adjust anything, right?
Normal wear conditions cause the valve clearance to get smaller over time, so noise isn't an indicator, and unless the bike starts showing symptoms of tight valves (low compression, hard starting, "lean" idle symptoms that the idle fuel mix can't address), there won't be anything that stands out screaming that you need to adjust them. Just do it every once in a while.
The process is shown in the manual:
...and gone over here: