Before I go into detail on why it works, here's the basic strat: Fast expand and use marines, hellions, missile turrets and bunkers as a mineral sinkhole while getting a deathball of Ravens, Banshees and Vikings.
OK, so the first thing you need to know is there is NO anti air (other than infested terrans and neural parasited stuff) that can kill a PDD, not Spore Crawlers, Mutas, Corrupters, nothing. Every PDD can take 20 shots, and ravens can cast two at full energy. Essentially this strat takes advantage of two things: first, that Zerg is usually not considered a good race for air units (with the notable exception of Mutas). I mean, nobody ever says "Skyzerg". Second, that Terrans are usually such tightwads with their gas that they never make Ravens. The Ravens should ONLY be used for PDDs. They take 100 energy to cast, which is a lot of in game time. This is why getting the Corvid Reactor upgrade is crucial. Also the Durable Materials and Hi-Sec Auto Tracking upgrades are useful, along with cloak. The reason this strat works is that even when your PDDs expire, you have complete air control, so your banshees can romp around killing things while cloaked because overseers immediately die to vikings. Zerg will probably either go mass hydra or mass infester to beat this. With mass hydra you can be cost effective with marines, and mass infester you just get a ghost academy. That's about it. You can nuke just for fun after you've roflstomped their main.
Anyway just a thought.
Tell me what you think ^^