I've got a similar problem with mine at the moment. I called the bike shop and they said they've had a few that require the stem adjustment at the 6000km mark. The damper tends to mask the effect, I could tell it straight up on my old '04 when it was getting a bit loose.
Anyhoo, make sure your stem bearings are correctly torqued then go from there. Remember, for the home mechs ... you have to tighten the two nuts *under* the top triple, not the big nut sitting on top. That's there just to hold the top triple on.
"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former." Albert Einstein
'85 GSX250S -> '96 ZX6R -> '98 ZX6R -> '00 ZX6R -> '03 CBR954RR -> '04 ZX10R -> '02 ZZR250 -> '06 ZX10R -> '08 KTM 990 ADV