According to a San Francisco IT consulting group, although DoubleClick does offer an opt-out page, this only affects cookies; DoubleClick continues to track users via IP addresses.
DoubleClick targets along various criteria. Targeting can be accomplished using IP addresses, business rules set by the client or by reference to information about users stored within cookies on their machines. Some of the types of information collected are:
In addition, the cookie information may be used to target ads based on the number of times the user has been exposed to any given message. This is known as "frequency capping".