I didn’t discover this feature of Google Spreadsheets on my own (http://www.readwriteweb.com/archives/googlelookup_wow.php for that), but I found it hard to imagine from the description what it did. It is more interesting to see than read about, so here’s a desktop video where I followed along with the instructions given by the link.
Demonstration of Google Lookup function in Google Docs spreadsheet on Vimeo.
