Hi,
while I like dia more than XFig because of it's cool GTK+
GUI, there are some features I miss desperately. Maybe I
just don't know, how to use dia rightly:
1. Hatches: XFig has all kind of lines and other patterns
to fill shapes with. In many cases this is better than
using colours, e.g. if it is for printing and no colour
printer available. I did not find any hatches in dia.
2. LaTeX special fonts: XFig allows to mark text as
"special". If exported to "Combined PS/LaTeX (both
parts)" the result can be included in a LaTeX document
while all fonts are the normal LaTeX fonts. This
makes the resulting DVI look very consistent. I did
not find this feature in dia.
3. Resizing of groups: XFig allows compound objects (or
groups in dia jargon) to be resized. I don't need to
explain why this is good :-) I didn't manage to resize
groups in dia.
4. Libraries: XFig has some interesting element libraries,
much like dia, but different. I don't know whether one
import them in dia, but that would be nice.
5. Stability: XFig is (at least for me) a little bit more
stable than dia.
Maybe these are some suggestions for dia, maybe some of the
functions are already there (but I did find them), or maybe
one could port good ol' XFig to GTK+? :-)
Cheers!