[joevandyk]

While I probably wouldn't store things in an array, it's useful to get data back out in array format sometimes.

    select array_agg(email_address), home_state from users group by home_state

Will give you a list of home states and all the email addresses that belong to that state.

[radiowave]

Right. A case I've used them for is a recursive query which returns a set of rows, where each row is some end-point that matches the query criteria, the rows can include arrays representing the list of nodes traversed to reach that end-point, or some notion of the path cost by hop.