The usual disclaimer... not a programmer, but perhaps some GSOC participant would find my suggestions worthy of implementation.
Inkscape has gained some pretty impressive features lately, but complexity has taken a toll on the UI. It now contains many icons, toolbars, and dialogs, and these UI elements take a lot of space, even on a large monitor. he problem is even more pronounced on an Ubuntu desktop where the GTK theme forces Inkscape to render all toolbars using extra large icons, making it too large for many resolutions. The dialogs are also too large, with oversized controls and a lot of spacing, and you can barely fit a couple of them on each side when they are docked.
Gimp had a similar problem and they solved it by introducing a "small" theme that users can st, which makes all the icons and widgets smaller. I think Inkscape could benefit from using such a theme.
Another great UI improvement would be to make inkscape remember the windows settings between sessions. Currently whenever I open a new session of Inkscape I have to resize the window and turn on a couple of dialogs - layers and fill & stroke. Then I have to resize the dialogs themselves because the layer dialog opens with hardly any space to show more than one layer. It would be great if Inkscape could remember those settings between sessions.
One last thing, a very small one - I think having layer dialog icon next to the other dialog icons on the right size of the main toolbar could be useful.