My whole world has changed. Thank you, evolution.

AND, it's not just for fun anymore:

"Is the G spot just for pleasure or does it have adaptive significance? An extensive series of studies in laboratory rats demonstrated that vaginal mechanical stimulation produced a strong pain blocking effect, stronger than 10 mg of morphine per kg of body weight. However, the most convincing evidence that vaginocervical stimulation blocks pain requires a verbal confirmation from women.

Consequently, we performed a series of studies in women, measuring pain thresholds during vaginal self-stimulation.

Pain thresholds were determined by applying a gradually increasing force to teach finger of one hand using a Ugo Basile Analgesia Meter. The subject places one finger on the 1 mm diameter point of the analgesia meter and a controlled, steadily increasing force is applied ranging from 0 grams to a maximum of 1 kg. The subject reports by saying "now," when the finger pain is first perceived (defined as "pain detection threshold") and by saying "stop," when finger pain becomes too uncomfortable to continue (defined as "pain tolerance threshold"). The pressure device is lifted from the finger when the subject says stop. Tactile thresholds are determined by applying a graded series of nylon monofilaments of varied stiffness (von Frey fibers) to the dorsal surface of the hand.

We found that the elevation in pain detection threshold increased by a mean of 47% when pressure was self-applied to the anterior vaginal wall (the Grafenberg spot). When stimulation was applied in a pleasurable manner, the pain threshold was greater (by 84%) than that in the resting control condition. The PD threshold increased by a mean of 107% when the women reported orgasm.

There were no increases in tactile (or touch) thresholds. This demonstrates that the effect was analgesic not an anesthetic effect and not a distracting effect. This analgesic effect was produced by pressure and by pleasurable self-stimulation applied to the anterior vaginal wall (G spot). (this was published in the Journal Pain., 1985, by Whipple and Komisaruk)

Pleasurable self-stimulation, but not pressure applied to other genital regions also produced an analgesic effect. (Published in Journal of Sex Research., 1988, Whipple and Komisaruk) It was then demonstrated that an analgesic effect also occurs naturally during labor.

We believe that childbirth would be more painful without this natural pain blocking effect, which is activated when the pelvic and hypogastric nerves are stimulated as the cervix dilates and from pressure in the vagina produced by the emerging fetus. (Published in International Journal of Nursing. Studies, 1990, Whipple et al)"

http://www.hisandherhealth.com/articles/Beyond_the_G_spot_Where_do_we_go_from_here.shtml