The taxi business is highly screened and monitored, and even there you can to some degree beat the system and channel money away from the government.
Simply don't turn on the meter, and work out a flat rate with the passenger.
Plus I think the Uber concept is very crappy. A buddy of mine does it on the side. He told me that his hourly income translates into something of around 10 bucks.
Which isn't horrendously bad, but it wouldn't be anything near enough, given he's in Boston.
I told him to stop fucking doing it, cause his vehicles usage expenses might eat up the few extra bucks he makes.