Often the small one offs.
in reply to The code I'm most proud of is:
Last week someone was struggling to merge a few hundred names and addresses into letters. His source was a Word doc containing a two column table. He fought Word but Word won. :-) I was able to knock it into a csv file and within half an hour he was merging with ease. Perl won!
It was satisfying that everyone told him, "Oh, give it to wfsp he'll sort that out." And he bought me a couple of pints. :-)
Now, as for the people who think a spreadsheet is squared paper...