Essentially, this enables the rogue to gain 3 (or 4-5 if Cheap Shot is used) combo points from his opener alone. If you also have 3 points Initiative and use this talent you will have a 75% chance of gaining 5 combo points using Cheap Shot.
Preparation will immediately finish the cooldown on premeditation.
Patch 1.12.0 (22-Aug-2006): Now instant cast with a 30-yard range.
Old: 1 second cast time, 5-yard range.
Patch 1.6.0 (12-Jul-2005): Fixed a bug where the combo points gained using the ability were not properly removed after the duration expired. Also increased range and duration.