I was noticing some shimmy in my 1-month-old XB-600. While stopped, I applied the front brake fully and rocked the bike forward and back. There was a distinct "clunk," indicating looseness in the steering tube bearings. (I also checked the triple clamp bolts, but they were adequately tight.)
Access to the bearing nuts is restricted, but I was able to tighten them up by tapping them gently on a land with a metal punch, with the lock nut tightened the same way, only with a bit more force.
Steering is much more positive now.
I am surprised this happened in 1 month, though I guess it would depend on how many miles and the terrain you ride on. I had this same thing at about 1000 miles. You don't really notice it until as you said a wobble or a clunking noise. But you will notice the difference after tightening the goose neck nut. I have made it part of my 1000 mile check up. Just rolled over 3700 so it is almost due again.
Happy scooting,
JamesS
I'm sure it was loose out of the box. That's why a shop will charge $100 for "setup." If they're earning their money they'll be checking the assembly.