uhh....yeah...tons of times. i have a very old friend that has now a whole list of disorders.
other people i have somewhat known include a bipolar, a mild adhd, two that were commited (which i only know they were because of the first mentioned old friend that was in the same place then), a girl that turned out having had voices in her head for a long time, one with AS that i a few years after i found that out spotted here on wrongplanet, and the girl that lives in the same house as me has some kind of personality disorder she said, but she refuses to tell me which one.
all these people i havent seen much often though..mostly vague acquaintences and distant friends, the only kinds i have. and they also exclude, of course, the millions of mentally disordered people i know through therapy and such.