Okay, most of my programming here at work is either PHP or Python. That said...

First, if you learn it, learn PHP-5. Wave of the present/very-near-future, and with enough differences from PHP-4 that when I say five I mean five.

Second, PHP is great for getting things out the door quickly, but it requires some real discipline in order to make a large project which isn't a nightmare to maintain and upgrade.

PHP5 helps with this by adding exceptions for error handling, which (from my Java experience) are Very Good Things when it comes to reliability. There are only so many decent ways to show that an error occurred using return values. My preference with PHP5 is in fact to use it like I might with Java--make most things an object, have a utility class that then has your "myCapitalization()" function instead of polluting the global namespace, etc.

I guess what I'm getting at is that if you're doing PHP for small one-off homepages, most of my advice here is needlessly clunky. But I often have to deal with a codebase of PHP code which has segments written more than four years ago, so I've seen the bad side of PHP in terms of maintainability. (Code using regular expressions to parse descriptive error messages to catch errors, etc.)

I'd place PHP in the realm of small-to-medium businesses and personal home pages. If that's the kind of work you would like to do, by all means, go for it. If the book (check your local library) isn't boring in the "I know that" sense or the "I can always check the API" sense, then it's probably worthwhile.