Deleted files

Files aren't deleted from the filesystem until 
All hard links to the file are removed from the filesystem, and
No processes have the file open

This is great for
Temporary files, only used by this process and possibly it's children.
Totally unaccessable files. 
Well, user and root can get at them via /proc/PID/fd/#

$ lsof -p 2487
CMD    PID USER   FD  TYPE DEVICE    SIZE   NODE NAME
prog  2487  bri   0u   CHR  136,5              7 /dev/pts/5
prog  2487  bri   1u   CHR  136,5              7 /dev/pts/5
prog  2487  bri   2u   CHR  136,5              7 /dev/pts/5
prog  2487  bri   3r   REG    3,5     627 115533 /tmp/foo
prog  2487  bri   5u   REG    3,5    5571 277062 /tmp/tmpfg3RD3J (deleted)
$ ls -l /tmp/tmpfg3RD3J
ls: /tmp/tmpfg3RD3J: No such file or directory