Sorcerers, wizards, magicians, and other practitioners of the magical arts may be found (in small numbers) across the World, if one knows where to look. They congregate in secret cabals where they work their wonders far away from the prying eyes of the Church and the superstitions of the common people. This is not to say that the art (or, if one prefers, science) of magic is proscribed, but the Church meddles too much and the peasantry have a difficult time distinguishing rightful practitioners from Witches.
Magic-Users claim to seek knowledge about the World and, if they're being watched by the Church, God's Creation. Despite this lofty goal, most practitioners spend their time in the pursuit of earthly pleasures. What use is knowledge if one gains nothing from it? Many a magician has been tempted by the loathsome devils which inhabit the netherworld. These creatures promise magical power that may fulfill even the most wicked desire and the most perverse of turpitudes. It is for this reason that the Church believes Magic-Users, when found, must at least be monitored if not burned immediately to prevent a scandal.
Those few who do actually use their powers to further their understanding of the world and its logos become rapped in bitter rivalries with other such scholars. Usually this has little to do with actual differing opinions, but rather the sorcerers fight over the limited magical resources of the World's kingdoms and the patronages of lords and kings and emperors. Because of this fact, Magic-Users are loathe to share their secrets with one another. Sadly, such rivalries slow the rate at which useful knowledge can be obtained, and few new spells or magic items have been created since the time of the Empire.
The Church also hinders progress. To take but one example, recently in the city of Lichgate four mages were burned at the stake simply because they wished to understand the process of decay and hired a few ne're do wells to exhume a number of corpses from the cathedral graveyard. The duke's soldiers who were tasked with the arrest of these men told terrible stories of undead servants and demonic guardians, but who is to believe such slander? The rabble will say anything to justify their ignorance!
Magic-Users have few friends in this world. The Church is ever wary of their propensity for temptation, the peasantry views them as simply conduits that demons use to steal their cattle and kill their children, and others of their own kind are just as likely to murder them as give them a handshake. Still, all of this power has to be good for something, and indeed many Magic-Users have ingrained themselves into the courts of the World. With this comes power, influence, and laboratory space.
A rough account of my house rules for Magic-Users may be found in this post. The only one not listed is the way I handle spell acquisition. Magic-Users will gain no spells automatically when they level. All spells must either be gained from earthly or unearthly tutors, spell scrolls, or magical research. Magic-Users can have any number of spells in their spell books, but -- obviously -- may only memorize a number dependent on their level as per S&W.