From my experience, it is slow on every platform. I once wanted to make some vector art illustrations for a book a friend was working on, and ended up doing high-resolution raster graphics in GIMP instead because the vector graphics tools I tried (mainly Inkscape, because it had the best reviews) were either buggy or too painfully slow to use.
There is acknowledgement of slowness from the Inkscape dev team and some optimization efforts are underway, but they most likely won't land until 1.3.
If you're comfortable with outline view, that is a good way of speeding things up. However, for drawing it's a lot easier to rely on a raster sketch and then to trace the result in Inkscape either with the fill bucket or using the technical drawing and tweak tools. As of right now my experiences suggest that it's in a state where direct content creation can be really awkward, but it's very good for tracing and finishing images.
It's fast on Linux and Windows for me (no Mac experience), and I use it quite a bit. It does have some annoying limited precision behaviour in GUI input fields though, always (?) rounding to a small number of decimal places. This is problematic when you're doing things like rotating by 1/7 of a turn and need things to line up.