I used Inkscape for quite a while before finally caving in and getting Illustrator - it is a pretty good program with a decent feature set. Having said that, it suffers from the same problem I found with GIMP - i.e. the interface is not the most user-friendly and is most definitely not mac-like. However, for free programs they are excellent, and if you are not going to splash out on PS/Illustrator then they are probably worth the effort.