I started using Inkscape in 2007, however I haven't kept up to date with the latest versions.
When I tried out the GIMP and Adobe Photoshop, both in 2006, I always preferred Photoshop, but the same did not apply to Illustrator. I found Illustrator, although powerful, was much harder to learn and slower to accomplish most tasks when compared to Inkscape. The fact that it is open-source and uses the SVG standard further heightens my respect for the program and its developers.
The only difficulty I found with the program, when I was using it, was the rather awkward gradient tool. Hopefully this feature has improved.
I can remember writing tutorials for Inkscape, though sadly I don't have the time to write anymore. If you're interested in learning Inkscape, check out Pixel2Life's dedicated Inkscape section:
http://www.pixel2life.com/tutorials/inkscape/