Seamus Donohue's Random Tip of the Day: Know your cloaking devices!
Cloaking devices are high-slot modules that, when activated, make your ship invisible. You don't appear on the overview, you don't appear on the Directional Scanner, and you don't appear on probe scans. However, not all cloaking devices are the same, so it's important to know the differences.
Not counting variations, there are only three kinds of cloaking devices:
Prototype Cloaking Device I
Improved Cloaking Device II
Covert Ops Cloaking Device II
The Prototype and Improved versions, when active, both cripple your sublight velocity: the Prototype by 90%, and the Improved by 75%. So, the moment you turn on that cloaking device, you are essentially webifying yourself to 1/10 or 1/4 speed. Additionally, you cannot warp while cloaked, so if you want to go to warp, you have to drop the cloak. Also, the Prototype and Improved cloaking devices reduce your scan resolution just from being fit to your ship. So, if you have a cloaking device attached to your ship, you will targetlock things more slowly.
The Covert Ops Cloaking Device II (also known as a "covops cloak") doesn't have the velocity or scan resolution disadvantages, and you can warp while cloaked. However, it requires 10,000 teraflops to fit to your ship. There's a problem: no ship actually has 10,000 teraflops of CPU, so only ships whose descriptions say "reduced need for cloaking device" can use a covops cloak: Covert Ops frigates (both the probe scan variety and the stealth bomber variety), Recon Ships (the Force Recon variety only, NOT the Combat Recon variety), Transport Ships (the Blockade Runner variety only, NOT the Deep Space Transport variety), and Strategic Cruisers (but ONLY if they have an "Offensive - Covert Reconfiguration" subsystem fit).
Generally speaking, if you are flying a ship that can use a covops cloak, then it is extremely important that you do use a covops cloak. To do otherwise defeats the purpose of the ship that you are flying. Do not mistake the Prototype or Improved cloaking devices for the Covert Ops Cloaking Device II, as the Prototype and Improved will not let you warp while cloaked.