I have worn out a few keyboards on my iBook and if this problem is on your PowerBook then I might be able to help.
Pry off the key (the way the Apple manual/pdf states) and play with the rubber nipple underneath the key, sometimes they get a little stretched or out of place. This might help.
If its still killing you, try a tiny bit of silica based lubricant (Dont spray it directly on the key, use a q-tip on the mettle parts. Also, make sure that the lubricant wont dissolve the plastic or rubber parts.) If it is the key actuator (the switch underneath the key, then you might not be able to fix it.
If the key fails or intermittently works

, and you are under Apple Care, call Apple. Go through their steps to rectify the problem. They will likely ask you if you are comfortable changing the keyboard out on your own. Its really easy. Just send them back the defective keyboard with the box they provide.
If the key doesnt fail, then just turn up the music and type to that funky squeak beat. You can become DJ Apple-O
