The OO support absolutely sucks. No privitization of variables. No multiple inheritance. It's a performance killer.

Too many damn functions to do every little thing. I'm surprised they don't have a sort_an_array_by_the_values_second_character_if_it_is_after_2_pm() function.

no built-in database extraction

ever changing syntax. from minor point release to minor point release, functions change and break code (look at the manual for entires like "<4.0.3 use xxx. >= 4.0.3 use xxx"). That's damn obnoxious

Socket support keeps changing. Granted it's marked as an experimental module, but the interface has changed between 4.06 and 4.1.x, and between 4.1.x and 4.2.x. It's annoying. We can't upgrade to the latest php because socket use in all our code will break.

Doesn't have Perl's felxibility.

Regex work is clumsy

no map and grep (actually i hear that something similar may now be in there as of a few point releases ago, i havent checked)

that's a few that come to the top of my mind. PHP does have good points too, but to me it's more of a toy language at times.