I would like to make an addition to the previously posted answer:
The lost+found directories
To exclude the lost+found directories across all VOBs you can modify the previously proposed selection rule to be more generic:
#Skip the lost+found directories
element .../lost+found -none
However, using the '-none' flag causes the Windows ClearCase client to list errors when updating a snapshot view:
Unable to load "lost+found": no version selected in configuration specification.
Unable to load "lost+found".
It also does not properly unload any previously loaded folders or files, so you may need to recreate your snapshot view (or unload/reload the VOB) with the new selection rule if you really want to clean out the lost+found directories...
Elegance
For excluding any normal folder, the "elegant way" would be to specifically load the /main/0 version of the folder:
#Exclude the contents of a directory
element /VOB_name/folder_path /main/0
This will cause the folder to be loaded as empty and will not produce an error. It will also properly unload any loaded files. It unfortunately does not work for the lost+found directory, because it is always listed as version /main/0.