You should check your valve clearances after break-in (1-2 hrs on the bike) but 90% of the time, everything will probably still be in spec. After that, you might want to check the valve clearances every 10-15 rides, or if the bike ever becomes hard to start. My '03 has about 15 races and 20-25 play rides and, last time I checked, the valves were still in clearance, so no adjustments needed.
Checking the valves takes about 20-30 minutes and consists of pulling the valve cover, getting the piston at TDC, and sliding a feeler guage between the valve pullers and valve caps to see if the clearance for the exhaust and intake valves falls in the ranges listed in the manual. If they aren't, then you'll need to reshim to get them in clearance.