External library GD (used by PNG/JPEG/GIF drivers): Versions of libgd through 2.0.33 had various bugs in mapping the characters of Adobe's Symbol font. Also it was possible to trigger a library segfault if an anti-aliased line crosses an upper corner of the canvas.
External library PDFlib (used by PDF driver): Gnuplot can be linked against libpdf versions 4, 5, or 6. However, these versions differ in their handling of piped I/O. Therefore gnuplot scripts using piped output to PDF may work only for some versions of PDFlib.
External library svgalib (used by linux and vgagl driver): Requires gnuplot to be suid root (bad!) and has many bugs that are specific to the video card or graphics driver used in X11.
Internationalization (locale settings): Gnuplot uses the C runtime library routine setlocale() to control locale-specific formatting of input and output number, times, and date strings. The locales available, and the level of support for locale features such as "thousands' grouping separator", depend on the internationalization support provided by your individual machine.