Adam, First of all great work...
Absof#ckinbrilliant... Said it before, and said it again
A complementary program for Unix, Windows and Linux, which is also freeware GPL, that I can recommend, is
ImageMagick, which is a commandline utilty to convert among others SVG files to whatever format you like..
It has a wide API, including support for PHP, Perl, C, C#, Python and many more, so it could be incorporated on a website to convert the resulting GPSVisualizer SVG/gif combo to a plain gif, or JPG, or even PDF. You might take a look at it, and consider incorporating it on gpsvisualizer.
Others can use it at home like I do, to convert the maps to a rasterformat for inclusion on a html page etc...
Just my 0.02€'s worth.
Dutch