There's really nothing hard about using vectors; they'll just be blurry because they're probably not pixel-fitted. Also, complex icons are much smaller and faster to render in raster format.
One other facet of vector graphics, they don't always look that great at all scales.
I seem to recall a graphics designer blog that compared a vector to an image that was tweaked at the same scale resolutions. The differences were staggering. I don't think vector graphics are a panacea anymore. I'll see if I can find the link, was rather eye opening.
One of the big things I noticed in the first link there was that a SVG icon scaled to different sizes didn't look as good as a hand-optimised set of raster icons, largely due to issues that could conceivable be addressed. e.g. When the SVG icon was scaled, the lines defining the shape also scaled up in thickness so that they appeared far too chunky in the largest version. What if line-width were kept constant as the SVG was scaled?
While that link makes me appreciate that SVG speficially might be hard to work with and that simply scaling everything proportionally might not make for good icons across all sizes, I remain unconvinced that vector icons are hopeless. Perhaps SVG's have the ability to do what I describe above, or perhaps we need a more powerful vector graphics format to work with.
