UPS = Under Paid Slaves.
it all depends on the driver and the route. If the driver has lots of businesses, he/she (gotta be PC now-a-days) will deliver the businesses first, then pick up businesses before 5pm, THEN get to residentials. If the driver has a decent mix, then the driver will try to empty out the package car of ALL packages , then go back for business pick-ups. Businesses tend to have stricter time constraints than residentials... besides, if you work, you don't want your package sitting on your door step for several hours before you get home, increased chance of theft.
Keep in mind these drivers have between 100 and 200 stops per day.
-Steve (ex-UPS'er)