1. "Traditional" Kabbalistic Practice ~ As depicted in the Zohar, kabbalistic practice involves close textual analysis of the Torah. Each letter is important and a number of arcane techniques are permitted in this analysis. For example, because Hebrew script does not notate vowels, the same word can be read in a variety of ways. Connections between words in different parts of the Torah are imbued with meaning. Complex techniques utilizing the correspondence between Hebrew letters and numbers are employed (i.e. Gematria). Although the purported purpose of this practice was to reveal the different manifestations of God (the Sephiroth) as concealed in the holy text of the Torah, scholars (e.g. Scholem) have speculated it also served a meditative function. By focusing all their thought on increasingly involved and arcane readings of a passage, kabbalists whipped themselves into a mystical frenzy or trance. Under this interpretation, these traditional practices are ambiguous between the metaphysical and psychological interpretations of kabbalah. Is the trance of textual analysis a contact with the external divine? ~ or is it a delving into those aspects of the divine which can be discovered within?
2. Magickal "Qabbalistic" Practice ~ Western magick utilizes a series of rituals to effect journeys to the various "spheres" or Sephirah on the Tree of Life. Each sphere signifies a different grade in the acolyte's magickal progress. Traversal of the spheres can be a long and laborious journey; Crowley, for example, began his magickal work as a neophyte in 1898, but only achieved the rank of "magus" with his visit to Chokhmah in 1915. The ritual associated with a particular sphere involves the use of the substances and imagery which correspond to that sphere. Thus, as Hesed corresponds to the element of fire and the color white, the ritual associated with it may require that the acolyte dresses in white and keeps fires burning in braziers. The image associated with Hesed is of a crowned and enthroned king, and the acolyte may be required to fix his mind upon this image while performing the ritual. Chanting, complex movements, and (occasionally) psychedelic drugs are employed to induce a mystical frenzy of hallucinations in the acolyte. Magickal kabbalah also involves a "practical" aspect, i.e. it can ostensibly be used to effect changes in the world. In this case, the adept invokes the sphere which corresponds appropriately with the type of change he desires to effect. Thus, if the adept wishes retribution and judgment to fall upon a business partner who has cheated him (say, to pick an occurrance which seems unusually frequent in the annals of Western magick), he may invoke Geburah, which corresponds to judgment. Even in the literature on "practical" kabbalah, however, there is a deep ambiguity. The rituals which ostensibly effect change in the world can often be interpreted instead as effecting change in the adept himself. Thus, even magickal kabbalistic practices can be consonant with the psychological interpretation of the kabbalah.
3. "Hollywood" Kabbalah ~ The recent popularity of kabbalah in Hollywood has little to do with either of the above traditions and a lot to do with traditional cult conversion techniques (c.f., for example, this personal testimony). Yossi Klein Halevi says it better than I could:
The [Kabbalah] Centre is hardly the first California-based faith to combine self-help techniques, a smattering of postmodern physics, and Star Wars spirituality (the "emperor of evil" versus the "light force"). But, unlike, say, Scientology, the Centre has co-opted one of the world's great mystical traditions. It draws on just enough authentic Kabbalah to make the deception credible to the credulous. Concepts like the evil eye and blessed water do exist in Jewish mysticism, but they are Kabbalah's least spiritual and intellectual elements. And that's precisely why the Centre is promoting them as Kabbalah's essence. In fact, the Centre doesn't merely trivialize Kabbalah; it inverts its intention. In traditional Kabbalistic meditation on the names of G-d, the goal is to transcend the separated self and experience oneness. "It's about annihilating the ego, not reinforcing it," notes Pinchas Giller, professor of Kabbalah at the University of Judaism in Los Angeles.
Suffice to say, the Kabbalah Centre supports the discredited first century AD theory of Zohar authorship, attributes Platonic philosophy and Newtonian optics to kabbalistic study, and claims that AIDs is caused by nuclear waste. Furthermore, the Kabbalah Centre teaches that mere possession of its ($415) Zohar brings spiritual and material benefit:
The Zohar is not merely paper and ink. It’s the truth, and as such is alive with divine energy and is the ultimate instrument for generating miracles. An amazing number of people have reported them just from housing a copy of it in their home. By simply possessing the books, power, protection, and fulfillment came into their lives. You may find that hard to believe, but that’s before you owned a set.
Interestingly, the Kabbalah Centre's store does not direct one to the new critical translation of the Zohar currently being undertaken by Daniel Matt (perhaps versions published by other organizations lack the divine power of the Kabbalah Centre's edition . . . ?).
(1) and (2) are both complex and difficult practices, involving years of study, asceticism, and hard work. Whether any benefit can actually be achieved from these endeavors depends upon one's expectations. Certainly the Spanish kabbalists of the 13th century derived spritual fulfilment from their rituals, but it is doubtful that they achieved either the material success or physical immortality promised to practitioners of (3). Furthermore, although (2) and (3) involve progression through stages of spritual development, these are measured by onerous tasks in (2), but monetary contribution in (3). Only (3) claims any benefit from mere monetary outlay (such as simple purchase of the Zohar), and as such may be discredited as a serious interpretation of kabbalistic practice.