Are gyrocopters good, i have never seen one being used in combat..... or used well

They are, but not in or against all armies.

They are the only unit in the army that can reliably be used to march block enemies, letting you either split the enemy line if you're depending on combat, or slow it down for more turns of shooting.

Its flight move is also good for wiping out fleeing units, and the Steam Gun can cause a fair number of casualties on T3 units, or wipe out warmachine crews with a bit of luck.

It can be a great addition to your army, as long as you're not trying to use it as a mainline unit. It's best used in an entirely supporting role, and if it gets into combat at all, you've probably done something wrong.

I agree

One of the things I like about the gyro, is that it makes your opponent worry about it. Just use it as a threath.

I have always found that one is quite weak and easily dealt with but 2 gyro's are an infinately more dangerous prospect to face.
A tactic that they are useful for is the reverse overrun. If you are facing a frenzied unit or ubernasty then fly into the rearof them. Because of the frenzy and the fact that the over run is in the first round of a combat then that unit will be forced to over run backwards or wherever you decide to lead them. A bit of careful movement is required but it can give your expensive units a breather and is somewhat unexpected.
The only thing that I would send it into combat with would be lone sorcerers and even then it would be dodgy