I don't know if someone has already mentioned this, but have they changed the mechanics of creep to where terran/toss can build on creep? If not I don't see creep drop lasting long for normal overlords.
Depending on how long the dropped creep lasts, zerg can basically deny terran/toss expo like... forever, not to mention preventing wall-ins, and damaging standing buildings. With the 30% movement speed bonus, I can see high-level players like Jaedong and Savior completely covering the map with creep, blocking off/delaying expos and providing virtually infinite exits for their Nydus network.
I can even see mass offensive queen builds/rushes because of creep. I don't see a couple zealots or a bunker/depot/barracks wall in stopping two queens and six lings, especially since the queens can creep tumor their path to your opponents main.
Mid game queen drop/nydus with razor plague might be quite devastating also if razor plague makes it past beta. Drop two plagues on both exits of the mineral patch and move them in toward each other... ouch! then just dive back into the nydus network till mana regens enough to do it again... to all the other expos... lol
Just theorycrafting, but i don't think in alpha play to this point anyone has really tried to abuse this type of rushing/harassment.