Unfortunately, the answers aren't always accurate and it would be useful to choose a different result or to edit the existing one. A recent Google Spreadsheet update added a way to change the answer: click on the cell you want to edit, select "More options" and choose one of the other two alternative answers. Maybe Google will go one step further and provide an interface for editing the facts or flagging the facts that are inaccurate.
To use GoogleLookup, create a Google Spreadsheet and type in a cell:
=GoogleLookup("name", "attribute")
Some examples:
=GoogleLookup("Quebec", "population")
=GoogleLookup("Google", "employees")
Google Spreadsheets has a special function that returns information related to the Men's and Women's NCAA Division I Basketball Championship in the US and there's also a function for stock market quotes.
Homework: Create a spreadsheet that displays facts about 20 people, companies or geographical locations by using the Google Sets-powered AutoFill feature to generate the list of entities and GoogleLookup to find the facts. You can make the spreadsheet public and share the address in the comments.