It should probally be noted that if the zerg player had gone for hydras or ultras chances are he would not have bee able to spawn sooo many nydus worms.
Nydus Network Vid
It is very obvious when a nydus worm pops up somewhere as everyone can hear it. Similar to a ghost launching a nuke. I see overlords dropping things as more effective in most cases. As far as transporting units to the enemy base ect. however, I have some ideas for the nydus network as a whole.
Saving drones from harrasment.
Obviously a toss/terran opponent does not want a zerg player sitting on the same number of mining bases as them let alone more. So they will attempt to disrupt your expantions at every chance they get. 2 good examples of drone harrasment are templar drops or hellion drops(run-by). Why not build a nydus network in your main and have a worm pop out nearby your resource lines if you are keeping up with your creep tumors and overlord placements you should have advanced knowledge of an incoming harrasment. Just before the harassment comes tell all of your drones to load up in the worm. Even if the worm and the hatchery go down you are no where near as badly put back as you would have been previously without running the drones. If your drones stay then you lose the drones and the hatchery but insta teleporting your drones away even if you lose the hatchery in the process seems like it would be worth the investment of a 100/100 worm per expansion.
Assistance in an overlord drop.
It is pretty obvious to me why people opt for drops instead of nydusing and that's if your opponent notices the worm attempting to spawn... well he can pretty easilly stop it (just don't tell that to kungfuukitten
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Well pop out nydus worms on the opposite side you are wanting to drop from this should draw the majority of the opponent away from the drop spot. Also as discussed already the problem with a nydus worm spawning as opposed to a drop is they can usually kill it before it spawns.
Let's say you drop your opponents island expansion but while you are there your opponent decides, "I'll just go eliminate the zerg player real quick while he is attacking that island." This thought process could be very troublesome for a zerg player. But if you already have dropped and eliminated most of the defenses then spawning a worm is relatively safe so as you are finishing of the expo spawn the worm and then teleport to whichever spot your opponent is hitting as opposed to loading up and flying all the way across the map again.
Simply to distract your opponent.
This is just a short point it may not work in the pro level but I've seen it work with nukes before (which btw are also 100/100). Just start building a worm outside of your opponents sight range just the fact that he/she hears it should make them worry.
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Edit:
Base linkage
This one may seem very obvious but it came to my attention to mention it after Luminox made a post.
As the zerg get more and more bases their production facilities get spread further and further apart. If your opponent hits you with a 2 pronged attack, one whose purpose is to delay reinforcements and the other to hit your main either the forces in the main or the forces that are reinforcing from the expos will die or get delayed from reaching the other allowing the opponent to do more damage. If you have a network up you can just rally your hatcheries to your worm in each base so you are always engaging the enemy with your full strength (similar to the nydus canal in BW)
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Edit:
Harass Preventing
Unless your opponent is being very agressive in killing your spotting overlords and creep tumors you should if you are observant enough see any potential harasses coming in. If your army is nearby on creep while it can move in to intercept the harass (whether or not the harass is a drop, warp in hellion runby is irrelevant). But say your spotters notice 2 medivacs moving in to your gold expo on desert Oasis on the right side of the map and the majority of your army has just killed off the enemies natural on the bottom left side of the map. At the current time that's all you have for an army and you can't afford to lose your gold atm as it is your only mining expo. Spawn 2 worms (as the drop is still incoming so you have time to spawn a worm). One behind your forces that just killed the enemy expo and one somewhere near your gold expo preferably on creep so you get the movement bonus. Your forces should arrive in time to defend the expo.
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related links
Burrow