Normally I take the wheels in to get new tyres because it saves me $15 per wheel (ie. they fit the tyres for free) and I normally get the rego check done at my local servo by a car mechanic.
I had been noticing that my front tyre was always wearing asymmetrically - noticeably so - but figured it must just be the big roundabouts (shrug).
Well... after paying for the tyres and rego check, the guys in the shop tell me it should be right to go so I duck into the workshop to take it home and the mechanic has got a spanner on my headset bolt

That was a few weeks ago now and I've had time to get used to the "looseness" of the steering. OMFG its like riding a different bike - every single time I get onto it I'm smiling from ear to ear.
Sometimes its the simple things in life....

Moral of the story for me is that you really need to get someone else - who knows bikes - to once over your bike every now and then. There's every chance they'll notice something wrong that you thought was normal.