The history channel had an interesting show last night about a family
in Spain who made roughly $1.5 million playing roulette. This was
from about 1993-97, and mainly in European casinos.
The father developed a computer program to analyze the "number
history" of a wheel, searching for a bias and the favored numbers.
Thousands of number samples were required, so it took quite a while
to collect the history. The story left the impression nearly every
wheel has bias, and in some it is large enough to overcome the house
advantage. Once they knew the bias, and its size, he and his family
(6-8 total) would play day in and day out, gradually increasing their
bets as the wins slowly mounted (the initial stake was about $2000).
Eventually they were banned in all the major European casinos, so
they came to Las Vegas. They were also successful here, but the
father had a "stress attack" so they went back to Spain and stopped
playing.
Based on this account, I wouldn't be surprised if there are people in
LV who do the same thing, quietly, so as not to attract attention.
Many casinos even make it easy to collect the history data, by
displaying the last 20-30 numbers drawn. And it appears to be
entirely legal!