While descending a hill yesterday, I noticed some chatter in the front brake. Since I don't want my bike to go into the dance of death when I least need it, I stopped and quickly discovered my headset was loose.

I tightened it but if I load the bike and hit the brakes, it still feels like there is a bit of give in the system. Unloaded, you can't tell. It's not something you can really see and is definitely not as much as .5mm, but you can feel it. Braking feels way better, but if you hit them hard, you can feel a bit of give.

Presumably, it's going to feel like there's a bit more give than there would be if you tried to move your seatpost back and forth, but how much is too much? I had someone look at it and was told it's fine, but now I'm paranoid.

Squeeze the front brake lever and rock the bike back and forth. If it clunks, it's too loose. Keep tightening the top cap an eighth of a turn at a time until the clunk goes away.

Alternately...sit on bike, put front tire against wall (or other immovable object), and see if the steer tube rocks in the headtube by pushing back and forth. If it does, tighten headset. If not, you're fine.

There is definitely no clunk -- I was trying to figure out how I can distinguish flex in the system from worn bearings. It does not really rock when I push on it. Just for the heck of it, I temporarily overtorqued it on purpose just to see if it reduced what I was detecting and it didn't.

I've done so little climbing this year that my descending is total crap and I've lost my sense for how things should feel. Yesterday, I managed to momentarily lock my rear when a chipmunk attempted to commit suicide when I was going 37mph through some curves. The tire slid probably only a few inches before I regained proper control, but I can't even remember making a mistake that stupid before.

You loosened the stem bolts before tightening the top cap bolt, correct? Just want to make sure you adjusted the headset properly, as some forget the stem needs to be loosened to adjust preload on most headsets.

Your head tube is compromised, may have to buy a new bike

Completely loosened

Finally, some useful advice. I bought a new bike last year so I'm about due for my next one...

Make sure you provide enough preload on the bearings with the starnut before you tighten the top cap on.

Now THERE'S some good advice.

Didn't see one in there -- my fork seems to have a compression plug instead.

Uhhh...what?