I've read his "Ultimate Back Performance" book.
He doesn't think there are many exercises that a "qualified" athlete can't do. By "qualified" he seems to mean that the athlete has demonstrated the ability to perform that exercise under load with a neutral spine position and maintaining the abdominal brace.
A few people have suggested that doing some sort of low intensity strength training with spinal flexion might help reduce the intensity of spinal injury when it goes bad. I think Mel Siff might have mentioned that on the Supertraining list some years back, but I could be mistaken.
McGill is totally against the "sucking in the abs to activate the transverse abdominus" as well preferring the "bracing" technique.
Other than that, he's got a job where he flexes pig spines all day long and analyses what happens to them, and consults with a lot of different types of people about spinal injuries.
If you take anything away from McGill it should be:
Maintain a neutral spine, especially in day to day activities. Bad posture is accumulative with poorly performed exercises. Matt Spiller, a California physical therapist recommends using a rolled up towel everywhere...in you car, in your office, at home watching TV when someone complains of chronic back pain to keep the lower back in a arched position.
Matt Spiller's back rehab article based on the McKenzie techniques should be revisited as well. You can download the Volume 1, Issue 11 of Dan John's "Get Up" here:
The article is called "Press Up for Back Pain" and it's almost always what a therapist will have you do for an injured spine. I've seen this played out at least 15-20 times on the Power and Bulk. Someone complains of back pain or injury but insists it's not spinal. Matt Spiller recommends press ups and also says that it's probably referred pain from the spine. Poster scoffs. Two weeks to a month later, the poster sheepishly admits that his physician told him it was spinal, and his therapist recommended the McKenzie techniques, including the press up.