On the Difficulty of Conviction for Adultery under Shari'ah

I've been reading Hugh Kennedy's book, The Great Arab Conquests: How the Spread of Islam Changed the World We Live In. The book has a number of short anecdotes that illustrate various points that are interesting in their own right. Insha'allah, I'll share several of them as I go through the book, but I thought I'd start with one that is relevant to current non-Muslim fears about shari'ah.

One of the Islamophobe's fears is the punishment decreed for certain hudud crimes, an example of which is adultery:

In the Shafii, Hanbali, Hanafi and the Shia law schools the stoning is imposed for the married adulterer and his partner only if the crime is proven, either by four male adults eyewitnessing the actual sexual intercourse at the same time, or by self-confession. In the Maliki school of law, however, evidence of pregnancy also constitutes sufficient proof. ... Ayatollah Shirazi states that the proof for adultery is very hard to establish, because no one commits adultery in public unless they are irreverent. For the establishment of adultery, four witnesses "must have seen the act in its most intimate details, i.e. the penetration (like 'a stick disappearing in a kohl container,'" as the fiqh books specify). If their testimonies do not satisfy the requirements, they can be sentenced to eighty lashes for unfounded accusation of fornication.

However, what many non-Muslims don't understand is how difficult it is to actually convict a person of adultery and the severe consequences to those who do accuse another of adultery without being able to meet the very high standard of proof that shari'ah requires:

Mughīra [b. Shu'ba] was a tough and resourceful leader but his career was soon engulfed in a scandal that almost cost him his life.

He began an affair with a woman called Umm Jamīl, who was married to a man from the tribe of Thaqīf. Other members of the tribe caught wind of the affair and were determined to preserve the honour of their kin. They waited until he went to visit her and then crept up to see what was going on. They saw Mughīra and Umm Jamīl, both naked, he lying on top of her. They stole away and went to tell the caliph Umar. He in turn appointed the righteous Abū Mūsā al-Ash'arī to go and take over command in Basra and send Mughīra to him in Medina to be investigated. When he arrived Umar confronted him with the four witnesses. The first was emphatic about what he had seen: 'I saw him lying on the woman's front pressing into her and I saw him pushing in and withdrawing [his penis] as the applicator goes in and out of the make-up [kuhl] bottle.' The next two witnesses gave exactly the same testimony. Umar now turned to the fourth, the young Ziyād, who has already appeared [mentioned in the book] doing the army's accounts. The caliph hoped that his would not be the testimony to condemn a Companion of the Prophet to death. Ziyād showed a talent for diplomacy and quick thinking which was to serve him well in the rest of his life. 'I saw a scandalous sight,' he said, 'and I heard heavy breathing but I did not see whether he was actually penetrating her or not.' Since the Qur'an stipulates that conviction for adultery requires the unequivocal testimony of four witnesses, the case collapsed, and indeed we are told that Umar ordered that the other three witnesses be flogged for making unfounded allegations. The story was often repeated by Muslim lawyers, for here was the great Umar, after the Prophet himself the most important law giver in Sunni Islam, making conviction for adultery very problematic indeed.
-- pp. 125-6