Blow up:
The British Journal of Photography has published a detailed interpolation group-test. They interpolated megapixel photographs to 170-percent and 400-percent. The verdict? Genuine Fractals; crap on both tests. PhotoZoom S-Spline; clearly beats Adobe Photoshop at 400-percent, but not at 170-percent. So; use Photoshop bicubic if you only need to re-size up to 170-percent, or if you already have a 35mb+ image that only needs a short hop to get it up to a 50mb file-size.