Study published in the Journal of Urology, Volume 167, Issue 5, Pages 2113-2116 (May 2002).  The study's purpose was to determine the effect of the prepuce (foreskin) on sexual intercourse. The researchers examined sexual function outcomes in men who experienced sexual intercourse in the uncircumcised and circumcised states.

The study chose as subjects men who were circumcised for medical reasons. Only 7% of the men were circumcised as elective surgery. Even with such a large proportion of the subjects being circumcised for having problems with their foreskin, 38% reported that it was worse being circumcised.

Sex As Nature Intended It: The Most Important Thing You Need to Know About Making Love, is a book authored by Kristen O'Hara.

Chapter 8a, The Normal Thrusting Rhythm of the Natural Penis vs. The Abnormal Thrusting Rhythm of the Circumcised Penis: How It Affects a Woman's Sexual Pleasure during Intercourse is reproduced on the website.

I believe that once women come to realize how important the natural penis is to their sexual pleasure and love-relationship happiness, that the key to a woman's sexual ecstasy is the foreskin of the penis, that foreskin restoration by the man  will allow them to experience new joys from intercourse that they never thought possible, they will want their men to have foreskins.

Article published in Journal of the New Zealand Medical Association, September 12, 2003, Vol 116, No. 1181. Women reported that they are significantly more likely to experience vaginal dryness during sexual intercourse with circumcised men than with genitally intact men. The authors thought that the vaginal dryness becomes more apparent as women get older.

The authors concluded "Most likely, reported vaginal dryness and the related clinical designation female arousal disorder is but a normal female response to coitus with a man with an iatrogenically deficient penis." An iatrogenically deficient penis is one that has been circumcised.

Study published in BJUI (British Journal of Urology International), Volume 99, Issue 4, Pages 864-869 (March 2007). This is the Sorrells study. The Sorrels study is remarkable because it used objective measurements to determine fine-touch sensitivity of various parts of the intact penis and the circumcumcised penis, showing that circumcision removes the most sensitive parts of the penis.

Watch a YouTube video of Dr. Sorrells discussing the study and his results.

The Daily Loaf writes How to pleasure an uncircumcised man. Somewhat tongue in cheek and light on details, the article is nevertheless indicates that people are starting to learn about the foreskin.

Study published in International Journal of Epidemiology, April 2011. doi: 10.1093/ije/dyr104

Background One-third of the world’s men are circumcised, but little is known about possible sexual consequences of male circumcision. In Denmark (∼5% circumcised), we examined associations of male circumcision with a range of sexual measures in both sexes.
  
Results . . . circumcised men reported more partners and were more likely to report frequent orgasm difficulties after adjustment for potential confounding factors, and women with circumcised spouses more often reported incomplete sexual needs fulfilment and frequent sexual function difficulties overall, notably orgasm difficulties and dyspareunia.
  
Conclusions Circumcision was associated with frequent orgasm difficulties in Danish men and with a range of frequent sexual difficulties in women, notably orgasm difficulties, dyspareunia and a sense of incomplete sexual needs fulfilment.

A study published in Urologia Internationalis, Vol. 75, No. 1, 2005 (Urol Int 2005;75:62-66) (DOI: 10.1159/000085930). The authors assessed the effect of circumcision on sexually active men and the relative impact this may have on informed consent prior to surgery. 

The male subjects were circumcised for a benign desease. Penile sensation got worse for 18% of the men who got an adult circumcision. Only 61% of the men were satisfied with their adult circumcision. Considering that circumcision was for a disease, it is significant that not more men were satisfied with the cure.

Study published in British Journal of Urology (BJU Int.) 2009 Apr; 103(8):1096-103. Epub 2009 Feb 24. The study used a self-reported questionaire and reports on various genital and nongenital areas in terms of erotic sensitivity for intact men (uncircumcised).

Sex As Nature Intended It: Top 10 Ways Circumcised Sex Harms Women is a graphical guide that explains the mechanics of the sex act and illustrates the difference between intact sex and circumcised sex. This is a sexually graphic site.

The site linked above is an extension of the Sex As Nature Intended It site. The site is based on the book of the same name.

I learned a long time ago to tune out the hype in everything I read. There is a lot of hype on the Sex as Nature Intended It website. The authors try too hard to sell their ideas, and the website is very amateurish. But, when I look past the hype and read the explanations and look at the illustrations, I see a lot that I can relate to. Based on my experience and the shape of my penis, I see a lot of truth in what they describe. Before restoring, all my sex partners were usually sore after sex. As I, and my partners, got older, vaginal dryness became more of a problem and we always had to use lube. Foreskin restoration changed all that for me.

A page on the Sex as Nature Intended It website describing the sexual function of the foreskin. This page provides simple tests that people can take to see how the foreskin functions. For example, the page describes how to feel the difference between fine touch nerves and pressure sensitive nerves by touching the lips and cheeks. The intact penis has both fine touch nerves and pressure sensitive nerves. Unfortunately, circumcision removes much of the fine touch nerves and if the shaft skin is tight, prevents the proper stimulation of the pressure sensitive nerves.

Study published in the BJUI (British Journal of Urology International), Volume 99, Issue 3, Pages 619-622 (March 2007). The study showed that there was a loss of sexual pleasure and enjoyment for a significant percentage of men.

Paper published in BJUI (British Journal of Urology International), Volume 83, Suppl. 1, pages 79–84, (1999), and authored by K. O'Hara & J. O'Hara. The authors surveyed women having sexual experience with both circumcised and anatomically complete partners to determine if there were any differences in sexual enjoyment. They determined that circumcision results in a less satisfying sexual experience.