Stefan Mischook has posted another take on why he thinks PHP developers should learn object-oriented programming:

For people new to OOP and are comfortable with 'classic' procedural php, you may be wondering why should you even bother to learn object oriented concepts...why go through the trouble?

He has several suggestions included in the post like:

• PHP is moving in an OOP direction [...] So, to really understand and use these frameworks properly, you need to understand object oriented PHP.
• Object oriented PHP really begins to shine as the project becomes more complex, and when you have more than one person doing the programming.
• OOP is the modern way of software development and all the major languages [...] it only makes sense (in terms of career,) to keep your skills up-to-date.
• OOP based PHP is much easier to maintain and update

He also suggests a method for developers to get started with OOP in PHP - how to plan out a project and think in objects rather than procedurally.