during a recent weekday afternoon arrival at MIA, I stood in the immigration line (US Citizen) for more than an hour, then in the customs line for about 15 minutes (and this was because I had no checked luggage).

with checked luggage in Customs, it has often been my experience that even after waiting a long time upstairs in immigration, the checked luggage has still not come out downstairs in customs.

caveat emptor or whatever