Since Walter's added DW_LANG_D output to the DWARF debugging information, I've updated my GDB patch to add this information to GDB.

At this point, we've now got symbol demangling for linux D executables compiled with or without the -g option.  Finally making some progress. Now all we need is for Walter to fix the line number stuff.

Anyway, the patch can be had at: http://svn.dsource.org/projects/gdb-patches/downloads/gdb6.3/d-gdb0.2.patch

put it in the gdb-6.3 source directory and run:
patch -p1 < d-gdb0.2.patch

Then compile, and enjoy!