If it's possible your code will end up under intensive review during a Supreme Court trial, then you want to make sure to avoid global variables.
See this article:
Buggy breathalyzer code reflects importance of source review
There were some problems with the
style of the code that were identified
by both studies. One of the stylistic
issues that concerned the reviewers
was the extensive use of unprotected
global variables. This is considered
poor form because it increases the
risk that the program state will
become inconsistent or that values
will be inadvertently modified or
overwritten. The researchers also
expressed some concern about the fact
that decimal precision is not
maintained consistently throughout the
code.
Man, I bet those developers are wishing they hadn't used global variables!
