Hi folks!
Thanks for the feedback. While the usability of the icon on very dark backgrounds is indeed limited, taking away the blackness from the ink feels like taking away the essence. I've instead added added more of that blueish specular highlight [1]. With Tango we usually address this with the inner highlight, but it makes things look a little odd on the high-detail version. But you are right, a fairly monochrome icon will always have an issue on a specific background color.
I've also created a few OSX mimetype icons as requested[2]. I've pulled some of the mimetypes out of my, erm, pocket. So if you have a better mimetype:extension mapping than this [3], I'll fix.
cheers
[1] http://dl.getdropbox.com/u/24178/inkscape-app-icon-proposal.zip (same URL) [2] http://dl.getdropbox.com/u/24178/OSX-inkscape-mimetypes.tar.bz2 [3] http://dl.getdropbox.com/u/24178/filetypes.yaml