You do realize what bike couriers are paid, right? You don't just start off working for a big, top-paying service in NYC getting $3, $5, or $10 per delivery. I've talked to some here who said they had to start off working for a piece of crap company making $0.50 per delivery until they established a reputation and work history for themselves and could move on to something better.
I love riding bike around the city too but when it has been 16 degrees with an 8 degree windchill after a snowfall here and I see messengers at 7AM shivering at a traffic light so they can drop off their package, I don't envy them.
I know it seems cool but...