Not that big ... that's a good book, by the way. Also, you need to consider that some hosts didn't even upgraded to the latest version of php. So go on learning from that book because it is a good one and you can check the manual at php.net to see exactly what are the differences from version to version :)

How big is the difference between the current version of PHP and PHP 5.3.5.

I have a PHP subject right now and I'm trying to do some advanced studying about the subject. The book I'm currently reading is PHP Visual Quickstart Guide and when the book was written, the PHP version was 5.3.5.

I'm worried that there might be big changes since the book was written and it would suck if I'm studying something that is already outdated.