If you guys go into that, I'd suggest leaving a path open for TikZ (text to embed pics in TeX, see here http://news.ycombinator.com/item?id=1204172 , about use in a graph theory book).
for what it is worth, i managed to check out your great work by using tulip's dot import to get tulip's tlp file format, which you support just fine. i like where the tool is going!
(I'm already working on a similar project. Feel free to shoot me an email at the address in my profile if you want to talk about it.)