My favorite strategy: the banshee rush! It's simple. Grab double geysers and starports first, then get cloak and rush in taking out the mineral flow. When playing in teams, have your partner follow up with the reinforcements. For further details, see my epic win replay
A cloaked banshee rush is an expensive endeavor. If scouted, it becomes an absolute waste of minerals, as a bit of static defense or AA could easily ruin your expensive, fragile banshees. That being said, if one is able to prevent scouting the double gas or early starport, then they can be a viable harassment unit. I would suggest using a banshee rush primarily against Zerg. Protoss can get out observers, revealing your banshees, and scouting your build. Terran can always suddenly scan your base, ruining your opportunity for surprise. If you build marines early (which you should), you can push away any rude overlords. Zerg players typically don't build overseers until late game. Hit them with 3 cloaked banshees and it is actually possible to destroy their hatchery/lair (shouldn't have a hive this early) before they get detection! So I do agree that banshee rushes are powerful, but very expensive and thus situational
