In the series, it is revealed to main protagonist Kyon (a schoolmate of Haruhi's) that Haruhi is essentially God, but is as of yet unaware of her powers. She has the ability to change things in the world that she wishes were different; only her innate common sense, as well as Kyon's constant bickering with her, serve to keep her wild fantasies in check.
Followers of Haruhiism are called haruhiists. This term is used affecionately amongst fellow fans. The term haruhite is supposedly more derogatory, in the vein of Narutard.
Suzumiya Haruhi no Yuutsu/Yuuutsu (The Melancholy of Suzumiya Haruhi) is the first of a series of 9 light novels penned by Nagaru Tanigawa. It was adapted by Kyoto Animation into anime form. A second season of the show was announced this year on 7/7/07 (the Tanabata festival).
Lucky Star, another anime produced by KyoAni, frequently references Haruhi.
"Yeah, I've seen all the dubs and subs of the series, and of course learned the dance, too. I'm definitely a haruhiist for life now."
"I lol'd so hard when Konata gave her that Brigade Chief armband! PRICELESS!"
Based off the Melancholy of Haruhi Suzumiya where the character Haruhi is God living life in high school. She can alter reality and create dead space without even knowing it.
The Haruhi of the religion is often subjected to uncannily good luck, strange occurrences, and anything of the sort. They are subjected to superiority complexes although they are unknowing of their powers.
The world can alter to their beliefs.
Disciples are the ones in the know of the Haruhi's real powers and often keep reality stable by keeping the Haruhi steady.
The Haruhi usually attracts non-humans as her disciples.
The Haruhi will usually have a buttmonkey whom they have taken a unusual liking to, for example, in the series it would be Kyon.