His list so far is:
- Turning "register globals" on
- using shot open tags
- using the ASP style of tagging
- single-line condition statements (without the curly braces)
- improper use of exit()
- assuming settings on a remote server
For each of the above options, he briefly covers his opinion as to why they're wrong and can cause some serious headaches down the line. Most advanced programmers out there know about most of these issues, and have learned to work without them.