Reasons not to get one for me are that cervical cancer is relatively rare and the rate of abnormal smears is relatively high. If you have an abnormal smear, the doctor will then want to do some sort of intervention- which might simply be another smear, but could be a biopsy or something more invasive, with more potential risk. The risk of abnormal results increases during and shortly after pregnancy. Also, young adults are more likely to have abnormal smears because of normal changes in their cervix. I believe where you are at in your cycle can also effect the results.
I think its worth looking at your risk factors for cervical cancer in determining if you want the procedure. Most cervical cancer is caused by HPV. HPV is a sexually transmitted disease. If you are not sexually active, or have only been with your partner, who has only been with you, then your risk is pretty low. On the other hand, if you'd had multiple high risk partners, your risk is higher. Certain kinds may run in families, so having a relative with cervical cancer might be a reason to get one as well.
Also, it might be worth looking into pap smear protocols in other countries. In the UK for instance, they do not begin testing until age 25, and then only test every 3 years. Older women only get tested every 5 years, and then not at all after 65. Here is a link to their website, which explains their reasoning. http://www.cancerscreening.nhs.uk/ce....html#eligible