I don't think you really mean "object orientation" so much as "a byzantine object hierarchy" (stereotypically associated with Java, of course). To me, Ruby's object-oriented string functions are a lot easier to keep track of than PHP's:

x.length vs strlen($x)

x.gsub('foo', 'bar') vs str_replace('foo', 'bar', $x)

x.strip vs trim($x)

x.upcase vs strtoupper($x)

All four of the PHP functions use a different form: strX, str_X, X, and strtoX. Some of this could be solved with consistent function names, like always using str_X, but then that makes me wonder why one wouldn't just want to have all string functions available as object-oriented methods on strings. Python takes a different tactic, and has a non-object-oriented len() method, but this isn't just used to get the length of a string, it will also get you the length of a list, tuple, or dictionary.