1. An intelligent planning system for calendars for dynamically detecting and correcting plan errors caused by calendar changes, comprising: a computer system comprising an input module, a storage module, a planning module and an output module; said input module further comprising means for receiving a plurality of task descriptions, each task description describing a task to be performed by the user of the system and including fixed tasks and floating tasks, the floating task having a duration that is less than the time period between an earliest start time and a latest stop time, wherein a planned start time of the floating task is determined by said planning module and is within the interval between the earliest start time and the latest stop time of the floating task minus the duration of the floating task; said storage module further comprises means for receiving said task descriptions from said input module and means for storing a current plan comprising the plurality of task descriptions; said planning module further comprising means for automatically detecting and correcting errors in the current plan that occur whenever the current plan is modified, the planning module further comprising means for adjusting one or more of the planned start time and the duration of the floating task to correct errors in the current plan; and said output module further comprising means for presenting the current plan information to the user.