I agree with everything said so far. I've been printing from Qimage for years now. I use the Pro version, and love the combination of the hybrid interpolation and smart sharpening. I make prints up to 24x36" and get comments all the time from other photographers on the image quality. I've done some comparisons between resizing in CS3 using Bicubic Smoother, Bicubic Sharper, and garden variety Bicubic, with output sharpening with the very fine PhotoKit Sharpen, compared to resizing on the fly with Hybrid and Smart Sharpen in Qimage. My impression is that visually, the Qimage prints range from as good as CS3 to smoother with fewer noticeable artifacts (and then, only with a loupe) than CS3.
But when you take into account that the enlarging and sharpening is done on the fly, with its savings in time, effort and hard drive space, Qimage is my winner.
Additionally, I soft-proof in CS3, adding adjustment layers when necessary. Qimage has softproof/original A-B capability that is as accurate as CS3's, and it reads the adjustment layers.