Hello Alexandre! Nice to hear that someone is working on the export dialog!
i won't claim knowledge of HIG (because i don't have) but my first impression of this mockup is that it can use more spacing, it looks too dense and busy
Actually I tried to make this palette as small as possible. The reason is simple: I hate large dialogs/palettes and I'm not the only one. One of most widespread complains about opensource software written in Gtk/Qt is that everything is huge and takes too much place on screen. E.g. look at "Resize image..." dialog in the GIMP. GIMP has gone through HIGification cycle, but still this dialog as larger than it could be.
Alexandre
But is the export dialog something that you have open all the time? I understand the need for small windows if it is something that you will have open most of the time, but is the export dialog really one of those? The drawbacks of small windows with little spacing is that they are
As Alan pointed out to me when I was redesigning the upcoming Preferences dialog, one should use headers and space rather than frames to separate content as described here: http://developer.gnome.org/projects/gup/hig/2.0/controls-frames.html
Also, did you read the suggestion of bitmap preview in the export dialog? http://sourceforge.net/tracker/index.php?func=detail&aid=1064371&gro... (I belive this is planned for, but if it's not, just forget about it)
BTW, great idea with the dropdown list, much better than the current implentation. - Andreas