Why doesn't X11/XQuartz start on Lion?
It appears that the GnuPlot package delivers an older version of libfreetype.6.dylib than is installed on Lion (or SnowLeopard, in my case).

otool -L /Applications/Gnuplot.app/Contents/Resources/lib/libfreetype.6.dylib 
/Applications/Gnuplot.app/Contents/Resources/lib/libfreetype.6.dylib:
    /tmp/gnuplot-i386/lib/libfreetype.6.dylib (compatibility version 13.0.0, current version 13.2.0)


Yet my error is that GnuPlot is trying to load "/usr/X11/lib/libfreetype.6.dylib" and not the library contained in the GnuPlot package. That library is the right version:

otool -L /usr/X11/lib/libfreetype.6.dylib 
/usr/X11/lib/libfreetype.6.dylib:
    /usr/X11/lib/libfreetype.6.dylib (compatibility version 14.0.0, current version 14.2.0)


This is as far as I have gotten. I did note that the library aliases in the GnuPlot package all point to the libraries delivered with GnuPlot (4/15/2011 in my case), so my next trick will be to create a new alias for libfreetype.6.dylib pointing to the one in /usr/X11/lib and see if I get a new error.

Maybe the answer is to build GnuPlot on our Macs?