I'm working on my third Inkscape illustration and one of the biggest problems with the application is the lack of ducumentation.

The Inkscape documentation page links to an unoffical (and very incomplete) manual by Kevin Wixon under the heading of 'Manuals' but I had completely over looked the heading above called 'Book' that links to A Guide to Inkscape by Tavmjong Bah.  I'm not sure why the latter is treated as a book but it is complete and highlights pretty much all of the features of Inkscape.

Another useful document for getting to know Inkscape is the Keys and Mouse reference. It would be easy to overlook this document as something just for hotkey freaks, but many of Inkscapes features are not accessible through a gui and only have hotkeys (i.e. how to reverse a gradient).

And the other overlooked resource is the Screenshots section. Check out the screenshots for all the versions of Inkscape to get an idea of what features Inkscape has under the hood.  Without looking at the screenshots I would not have known how to create a starfield or that you could move the centre of a radial blur away from the centre to create an asymmetric fill.

So whilst these resources are linked from the Inkscape site, I thought it was worth pointing out which of the resources you are most likely to find answers in.