They are mostly used when a condom breaks or other accidents occur. The temporary side effects are NOT pleasant for women, so they aren't going to be likely to take it on a regular basis.
Most women would be better off taking one of the many BC pills (or Depo shot) regularly. Yes, not every woman matches well with every pill, but if you provide the doctor with appropriate feedback, he/she can usually find the type and forumlation of pill that will work for you. This can take some trial-and-error, but in the long run it's the way to go.
Barriers are still necessary to reduce the chance of spreading STDs. If you haven't tried Durex Extra Sensitive condoms yet, you should. They are much better for both partners than anything else out there, unless one of them has a latex allergy.
-Troy