I have written some serious one-liner doozies in the past...usually when trying to do something somewhat complicated with a bunch of files. For example, one time I did a one-liner that recursively went through a directory tree and renamed files with certain names to match the directory name, or something like that.
Other one-liners I've used for doing recursive media conversion (WMA->MP3 for example), and of course for downloading Pr0n from various places with nice sequential filenames.
Probably my most frequently used BASH construct is the "while read" one:
Code:
cat /etc/passwd | awk -F: '{ print $1 }' | while read line; do echo $line; done;
And yes, I know that example does absolutely nothing useful, but it's an example.