X11 turns 25 today...

The guys over at Phoronix reminded me that X11 turns 25 today.  That's pretty awesome news.  X11 has been the basis for Windowing on Linux since windowing began there.  Many have tried to replace it but so for no one has.  It's modular focus has let it last this long and makes it really hard to supplant.

Let us know what your worst X11 configuration nightmare was?