Wow. My city just had the Cities XL version of a Dwarf Fortress tantrum spiral. And guessing by the way the city played out, it will inevitably happen to you on just about any map the game comes with if you decide to play single player. This is caused by the exorbitant prices charged by the AI for goods as well as some of the game's basic mechanics.
As far as I can tell, the best way to increase your economy is with offices and high tech industry. These generate plenty of revenue and jobs for higher income citizens. Unfortunately, for high tech industry to work properly, it needs manufacturing, waste removal, and offices. The last two aren't to hard, especially since offices will be aplenty if you are going for high tech/office city. Manufacturing, however, either needs to be created with highly polluting manufacturing (which themselves need highly polluting heavy industry) or bought from the NPC trader at the very high prices. The problem comes in when you realize that pollution harms the functioning of both offices and high tech industry, to the point where at a population of 500,000 all the high tech industry in the entire city shut down due to the pollution caused by the heavy industry and manufacturing. This in turn led all the offices (offices also need high tech; they are co-dependant) to shut down, leaving me with high unemployment, low citizen satisfaction, and a dwindling income.
After reaching a peak of about 600,000 citizens, the town fell apart, money went from over 1,000,000 in the back down into the negatives, and so I ended up having to delete it.