I like to keep my computer organized and this means that I like to keep my files and folders sorted alphabetically by name. Occasionally I might want to sort them temporarily by kind (i.e. PDF, JPEG, etc.) and afterwards I would sort them again by name. In Mac OS X Snow Leopard you had to toggle between one or the other manually and Leopard would only remember your last sort method selected.
Now Mac OS X Lion will let you decide how you want your files arranged and it remembers that arrangement, but it will also let you temporarily view them sorted in a different order. The next time you view the files they are sorted in the original method you selected, but in order to get this to work properly you need to know the difference between an old and new Finder view in Mac OS X Lion.
Mac OS X Lion introduces a new way to temporarily sort your files when viewing them in Finder. It is called Clean Up By and it is available when a Finder window is active on the Finder View menu. If you select it and then one if its sub-options: Name, Kind, Date Modified, Date Created, Size or Label your files are temporarily sorted in the selection you made.
The sort selected using Clean Up By is temporary and if you want to arrange the files permanently you need to use Arrange By from the View menu and one to its sub-options: Name, Kind, Application, Date Last Opened, Date Added, Date Modified, Date Created, Size, Label or None.
So the trick to remember is this: if you have a favorite sort method for your files select it with Arrange By and your files will always be sorted using the method you selected when you open the folder that contains them in Finder. If you desire to use another sort method temporarily while viewing your files in the folder that contains them you would use Clean Up By.