an overseer is cheap to make and even without overseer, a nuke cant deal too much damage to zerg, they dont have much static "things", their overlord move like snail but still manage to move out of the nuke area, and a nuke cant kill a hatchery, plus if you pay attention, u can see where the ghost is(even its hidden, kind of transparent), there are ways to deal with it, like a fungal growth, bane killing each other near the ghost, etc.
Added on September 30, 2010, 5:25 pmevery unit in the game got their advantages and disadvantages, roaches got theirs, they are pretty cheap, high hp, upgradeable speed, upgradeable skill for moving/healing while burrow, pretty useful in the correct hand, their disadvantages should be short attacking range, 2 food count, cant attack air, and its "heavy armor"(so marauder, siege tank, immortal, ultralisk can deal alot more damage on them.
unless its a short game, else u should not just using them, you need to mix unit, they are good at taking damage, should mix with hydra who do alot more damage, lesser hp and more expensive, defend your hydra with them.
150min 100 gas isnt what id consider cheap. especially the precious gas zerg needs for mutas/banes/infestors (or even utlra if ur there)
then, nukes dont really have to deal dmg DIRECTLY to deal dmg. good terrans (like myself in a replay that i should be posting days ago >.>) will put a nuke on a crucial position say a ramp, you are FORCED TO BACK OFF, and when you do, the terran's main force pushes up. imagine what kinda DAMAGE would that cause to you? it could be as bad as an instant GG. (ps: TLO pulled it off on GSL too.)