1.Science:
bioinformatics,
astronomy,
drug discovery,...
2.Business:
target marketing,
advertising,
customer modeling and CRM(Customer Relationship Management),
e-Commerce,
fraud detection,
investment,
manufacturing,
sports,
entertainment,
health care,
telecom(telephone and communications),...
3.Web:
search engines,
bots,...
4.Government:
anti-terrorism efforts,
law enforcement,
profiling tax cheaters,...