Inkscape now has tweaked toolbar size preferences. Why is this? Well the main thing is that it makes the UI more usable on Ubuntu again. There have been some ongoing issues with size, many of which are due to the use of custom toolbars from before GTK+ had stock ones.
A while back I added some options to use 'secondary toolbar' size for the main tools on the left (and the top bar also), but for some users that did not help. Between Inkscape 0.46 being released and me recently getting a laptop with a very small screen (thanks Dice and LugRadio Live), I've been getting more done on that front.
After seeing more bug report activity on it, especially from people running on fixed 1024x768 monitors, I tracked down a bit more. The main issue is that while Inkscape is properly respecting the user's GTK+ theme for sizes of icons, the people setting those themes up for Ubuntu, among others, had chosen to set the two toolbar icons sizes to the same. So switching from using the primary size to the secondary size did nothing to help, as it just switched from 24x24 to 24x24.
So on the one hand the theme designers are imposing their idea of how things will be pretty, but on the other we were facing imposing our idea on what would make things more functional. Either way seems bad. So after splitting this specific issue to its own bug (#221676), I settled in and added enough preferences so that now the end user can decide what they want to do, and on a per-platform basis.
The change reduced the minimum size from the old 652x735 to now be 600x583, just over a 20% reduction in vertical size required. The big gain there is that it should no longer be pushing things for Ubuntu users on lower-res LCD monitors. Additionally now when I flip over from OS X to Linux, I'll be able to keep the smaller icons showing up that make my workflow go faster.
Of course that does tend to mess with the crispness of some of the icons... but if people care about that they can just set the sizes back. In the long run we have plans to address that, but for now at least the work-arounds should be sufficient.