Can you still become an air courier and travel at a discount?

Air couriers are members of the general public who accompany time-sensitive cargo shipped as passenger baggage on scheduled airlines. That way, freight companies get expedited customs clearance and delivery. In return, couriers fly at 50 to 80 percent off regular coach fares. Sometime, they even fly free.
But, you have to be flexible in travel dates, and often must be ready to fly at the last minute, on the first flight out.
With concerns about terrorism these days, are air couriers such as I’ve described above still used anymore?