incoming former retail management weighing in.
The reason the day after Thanksgiving is called Black Friday goes back to accounting 101.
Normally losses are accounted for in red type in accounting programs, while profits are black. On the day after Thanksgiving, so much sales volume is done in one day that it can easily take retailers from being in the negative for the year, to actually making a profit, thus getting "out of the red". The impact of Black Friday sales is huge... however watch what you buy. Those $20 DVD players are usually pretty poorly made things that will fall apart after 4 months... but are perfect to have around for extra gifts for random friends/relatives that might show up to Holiday gatherings.
However for those of us who work/worked in retail, Black Friday had a whole different meaning... it was usually the most grueling and exhausting day of the year. Having to work the day after Thanksgiving when a lot of other people have the day off both interfered with personal/family plans, plus gave most employees a bit of bitterness about the whole thing.