[nxc18]

To make matters worse, most programmers don't really know regex well enough to use it without reference, and even if they think they do, they probably don't know the problem domain or the nature of their regex to get it bug-free. See basically all attempts at parsing email addresses in regex for an example of this.

Then you have the gotchas... E.g. most implementations have performance issues in many scenarios, leading to situations like when SO went down a few months ago.