I use SVG images almost exclusively in my apps, but there are downsides to SVGs:

...SVG compatibility is not good.
I too use SVG to define the splash screen and "help->about" image in my app, but use Inkscape to convert it to a PNG for the app. I tried using the SVG directly, but Qt doesn't have the compatibility needed to render it.

If you are using simple SVG, then it would probably work just fine for icons, at the cost of slower rendering and the need to deploy an extra library with your app. For more complex things, I think it is still better to use Inkscape to export the image to PNGs of various scales, and you choose the one that best matches the desired size at runtime.