Scan Once: Find all pictures once, but don't keep scanning.

If you have a large network drive, or if you have just a handful of pictures you want to see all over your hard drive, having Picasa scan these locations just once can make Picasa more responsive than setting the folders as Watched.  

Example: You have a network drive mounted as X: with pictures that you want to view in Picasa:

1.  Select Tools>Folder Manager

2.  In the Folder List, scroll to the X: drive

3.  Highlight the X: drive and select "Scan Once"

4.  Click OK

5.  Picasa will scan drive X: and its subfolders one time.  

Subsequent changes to files in drive X will not appear in Picasa unless you re-scan the drive.