- It uses macros instead of C++ templates in order to support ancient compilers.
- To handle events, you're supposed to make an enum for your controls and go through these EVENT_TABLE macros - it works, but generally it's a mess compared to nicer frameworks like Qt.
- Threading support is really lame, e.g. this quirk of AddPendingEvent: http://docs.wxwidgets.org/trunk/classwx_evt_handler.html#a07...
- Then and probably still today, OS X Retina support was completely broken. Not a great turnaround time - it was already a year after the release of Retina laptops.