There's an interesting post over at Balkinization. Eliot Spitzer's pecadillos were discovered when his bank reported suspicious transactions to the government, as they are required by law to do.
These events offer a window into a much larger phenomenon, the National Surveillance State, in which the state increasingly identifies and solves problems of governance through the collection, collation and analysis of information. Governments have always used information, but today's techniques are made more powerful and more prevalent by lower costs of computing and data storage.
If computing power increases enough, there is no reason why governments might not lower the threshold for reporting of suspicious transactions, or, indeed, require that every transaction over 100 dollars be reported. All this information could later be sifted through by data mining programs, in order to spot patterns of suspicious activity. The only limit is the technology and the manpower that law enforcement is willing to devote to analysis of financial transactions...
On the other hand, these developments carry all of the potential risks of a powerful National Surveillance State: Governments can make mistakes in assessing levels of criminality and dangerousness; and their data mining models may characterize innocent activity as suspicious. Without sufficient oversight and checking functions, government actors may misuse the additional knowledge they gain, for example, by instigating abusive prosecutions, or creating discriminatory systems for access to public and private services (like banks, airports, government entitlements and so on). And the more powerful government becomes in knowing what its citizens are doing, the easier it becomes for government to control people's behavior.
Remember, computing power isn't just increasing, it's increasing exponentially. Yet the government still manages to put our own Senators on terrorist watch lists.