First, Guy says "with few exceptions, all you should do is let people finish the day—maybe the week." I think most employers would not want the terminated employee (laid off, if you prefer) continuing in the workplace beyond the time they are given the news. Among others, employers often raise concerns of confidentiality and moral. That's not to say that the employer must be insensitive to the employee, the opposite is true. But keeping the employee around after the termination is delivered, more often than not creates problems.
Second, Guy says that Friday is the best day to do the layoff because they can use the weekend to decompress. I can see why he would say that, but in my experience, the terminated employee will use the weekend to get "tuned up". What ends up happening is that they can't get legal advice over the weekend. Family and friends, though meaning well and having their loved one's best interests at heart, will offer (often) unsolicited advice which (often) is wrong. Come Monday, expectations are through the roof, and the former employee is itching for a fight. So, the Monday, Tuesday or Wednesday termination is preferable.
I have a post called 12 Thoughts on Employee Terminations that gives you some of my thoughts.