I'm currently enrolled in Manhattan GMAT and find that it is only helpful on the basis that they provide quality study materials (i.e. tutorials and computer disks). The "tricks" they teach are standard and can be learned by talking to any experienced test taker. However, i chose Manhattan GMAT b/c Kaplan has the reputation of being unrealistic to the actual GMAT as they are trying to cover their asses by saying they "guarantee you increase your score"...therefore, they make everything more challenging than it should be. My experience has been that the best prep is obviously studying,studying,studying...only use the classes as a secondary support system.