Good Friend or Unwitting Enabler: When To Say No To An Addict

Close friends, family, loved ones, people in your life that you have come to accept for whatever faults they have - sometimes these people can become overwhelming burdons.  If you let them.  The family member with the gambling habit that always needs a loan, and never pays it back; the friend who always gets put out of an apartment and always needs a place to stay; the long time associate who likes to go a lot of places, never has car fare, but, while puffing on a costly cigarette, will habitually ask you for the money or for a ride.  Its good to be a good Samaritan, but when do you realize you are being taken advantage of by people who choose to create their own problems by not correcting their own bad habits?  If you say no, what happens if they have to come up with another means to get what they want?  Will you lose a friend? Should you care? Are you being too nice in the course of being a friend? When should you just say "NO"?