Undo Heaven, Just Add History States
If you are like me, and love having a good amount of undos in the event that you go overboard with your adjustments, you can change the amount of History States that you have in Photoshop CS3. Note that the location of the History States preference has changed as well.
Choose Photoshop>Preferences>General (PC: Edit>Preferences>General) and notice that there is now a Performance option on the left. You can change the History States in this area. Keep in mind though, if you are excessively using History States, you may want to rethink what you are doing wrong in the first place. I know I have to.