PHP 5 in general has been a good improvement over PHP 4, but those used to full blown object oriented program languages such as Java or C# may find some OO features still lacking in PHP 5.
PHP 5 has the usual things, such as classes, interfaces, abstract classes, inheritance, etc, but some useful programming constructs have been missing, though PHP 6, under development, aims to rectify that.
However, it seems that many of those features are going to be brought forward to the up-coming PHP 5.3 (which may make it more likely that it will get installed by web hosting companies sooner than they would likely go for PHP 6).
Sitepoint has an excellent summary of the features. The list of features include: Continue reading