When you see several people post as AnonymousDonor in a row, you generally don't assume they're the same person unless the conversational tone suggests it.  But that's changing through most of the Internet.

Starting in 2007, there seems to be a trend of lumping all anonymous posters everywhere into a gestalt being, depicted by an empty black suit standing with an imposing, confident demeanor.  Youtube videos abound with strange, disembodied, altered or synthesized voices making grandiose conspiratorial claims of invincibility through anonymity and numbers.  The effect is reminiscent of FightClub, though the only destructive acts attributed to Anonymous have been Internet-based harassment of various people who were judged to deserve it by whoever's reading /b/ at a given time.

The word "Anonymous" started to identify a group, rather than simply the status of a post or the author of an unknown book, thanks largely to a Fox-11 broadcast.  Confusion exists as to the events that led to the broadcast, but it is universally agreed that the story had so many inaccuracies as to be considered complete fiction.

The meme of Anonymous as a group has, as of 2008, been used to organize live protests against Scientology.  Protesters would wear masks, disguises and costumes, not only to mark themselves as part of Anonymous, but also to protect their identities from possible retaliation.  The use of memes from various anonymous image boards added to the character of the protests, for better or worse.