I know queens are good.
They have the spread larva and creep tumor abilities, which are really awesome. Also they have range AND can attack air units.
Every hatchery should have at least one.

That being said, i was only debating their ability as a fighting unit themselves.
They never struck me as doing that much damage (but i guess i only encountered one or two of them at a time), you can't reliably use them for offence (since they're so slow) they can only be built at Hatcheries (of which you'll have...4?5?) and take a long time to make.

If you lose 10 of them, how much time does it take to make them again?

Anyway i guess i'm wrong, and i've never seen mass queens actually played. i guess they can Transfuse each other for effective NI hit points (but i guess after a certain point a group of units can focus-fire one queen in one shot)