[Xuzz]

It's somewhat difficult to do DYLD_INSERT_LIBRARIES right on OSX; it tends to subtly break various system components even if your binary doesn't do anything. However, SIMBL (http://www.culater.net/software/SIMBL/SIMBL.php) usually works fine. (On the (jailbroken) iPhone, you'd want MobileSubstrate (http://iphonedevwiki.net/index.php/MobileSubstrate), which does use DLYD_INSERT_LIBRARIES, where it causes few to no issues.)

Also, when replacing methods, it's better to do it like this, by storing the actual function pointer to the implementation: http://pastie.org/private/nbaaog7hptyzsytahpc5a — it makes "stacked" overrides (imagine an app tried to hook the same thing as well, you don't want that to cause issues) safer than renaming.