The Bene Gesserit

• The Bene Gesserit are a secret society of women. There are no male Bene Gesserit, although there are males with minor Bene Gesserit training.
• Despite what they may have others believe, they serve no-one but themselves. They are not servants of the Padishah Emperor.
• The Bene Gesserit are NOT psychic. They may seem to read your mind, but they do this by use of petit betreyals - your own lack of control over your body language.
• Almost all of the Bene Gesserit's abilities come from the spice Melange. Prana-Bindu conditioning and the Wierding Way are the exception, but Other Memories are a result of use of Melange.
• Any human has the capability to perceive the flow of time differently, it's just that most don't realise this.
• Prescience can be unlocked by use of the spice, but it requires massive doses. Most humans don't have a high-enough tolerance to do this - they die first from spice poisoning. Extreme abilities may be unlocked by ingesting the incredibly toxic Water of Life - concentrated spice-essence extracted from a drowned sandworm.
• Women tend to have a higher spice-tolerance than men. Men who have a higher spice tolerance tend to have limited or no access to Other Memories, but often display a wild talent for uncontrolled prescience.
• Thus far, only women have had the spice tolerance and metabolic control required to ingest the Water of Life. The result is Other memories and limited Prescience. Every male who has tried to ingest the Water of Life has died, even with advanced Bene Gesserit training.
• The plan with the Kwisatz Haderach was to create a human male with an incredble tolerance for the spice. With an effectively unlimited threshold for spice tolerance, the beings prescient abilties would be similarly unlimited. Somthing similar happens with the Pre-Born.
• The Pre-Born are subjected to large amounts of spice in the womb. They gain access to Other Memories before birth, often with the result that they have precious little time to develop a personality of their own before they are swamped by those of their genetic heritage. Often they are subsumed and 'possessed' by an ancestors more dominant personality. The Bene Gesserit experimented with the idea as an alternate form of Other Memories but random possessions put paid to that, hence the name 'Abomination'. 

The School of Mentats

• Mentats are not from Bene Tleilax. The Tleilaxau are biologists and geneticists who can produce 'twisted' Mentats, but they are not the source of true Mentats.
• Mentats are human computers, capable of carrying out multiple independent calculations at the same time. They are capable of applying probability algorithms to every day situations. As a result they are capable of astounding leaps of insight, merely by calculating the variables in any given situation.
• Great Houses employ Mentats in a variety of roles, every thing from Spymaster or Strategist to something as simple as Diplomatic Advisor. There are very few (if any) independant Mentats.
• When a Mentat runs a computation or gathers variables, all semblances of emotion vanish as they turn themselves over to pure logic.

CHOAM and the Spacing Guild

• CHOAM is a trading cartel - the Emperor has a seat on the board of directors. They are not the Guild, they are a seperate and independant organisation.
• The Guild controls the Galactic Bank. This, along with control of space travel, makes them extremely powerful.
• Guild Highliners have foldspace drives. It is the vessel that performs the spacefold, not the Navigator. He navigates. Hence the name. It is not psychic teleportation.
• When a Highliner folds space, it requires either i) the ability to perform thousands of simultaneous calculations or ii) the ability to forsee dangers and navigate a course around them. Without doing either of these, a foldspace drive works, but you only have around a 50% probability of arriving safely at your destination. The first option is out of the question. Since Mentats cannot possibly perform that many simultaneous calculations, it requires use of a powerful computer, and that violates the Butlerian Proscriptions.
• Guild Navigators use gradually increasing amounts of the orange spice gas to grant them prescience. In this way, they gradually build up a tolerance to the spice, but it wreaks terrible changes in their bodies. They awaken their prescient abilities, and seem capable of scrying a short period into the future to perform such tasks as navigation and searching for individuals that may be hiding elsewhere. As extreme addicts, they come to rely on the spice gas to live, and without it they die very quickly. As a result, they live in sealed chambers for their entire lives. Their bodies are so warped that they require a suspensor field to move around.

 The Fremen

• Fremen stink to high heaven. They rarely wash (and then it's usually a sand bath), and they recycle all bodily fluids. To an outsider, a Fremen Sietch smells awful.
• Fremen are nocturnal - no native of Arrakis would be stupid enough to attempt a journey of any distance during the day. Travelling across the open bled during daylight hours is suicide.

Technology

• Stillsuits have a hood, and a face mask that covers the mouth and nose. It retains most of the moisture lost by the body if worn correctly. To make it work, you must walk around - the heels of the boots contain the suit's pumps.
• Hunter Seekers do not inject poison. They are basically sharpened slivers of metal, controlled by a magnetic field. They penetrate the body and then dig thier way along blood vessels and body cavities toward the heart or brain. It takes an excruciating minute or so to be killed by one. They can be dug out if you are quick, but the damn things keep moving around...
• Space Combat is expressly prohibited, upon pain of losing passenger charters on Guild Highliners.
• It is possible to use regular sublight drives to travel between systems. They are quite quick (it takes a few weeks to travel to a neighbouring system) but they are difficult to maintain and rather unreliable. People generally prefer Guild transport, even if it is quite expensive.
• Personal shields, when active, are visible as a light 'fuzzing'of the air around the wearer. They become more visible when they deflect an attack.
• Ornithopters have lightweight flapping wings. They are not flying boxes.
• In place of computers, which are totally prohibited, most people use either Servok mechanisms (finely tuned clockwork) or highly advanced radio control.