Updated (27/2/12): We have updated this page to include the mention of the 'white orbs' artifact.
While the Fujifilm X10's image clarity and ISO performance is excellent, we need to point out that the lens suffers from obvious vignetting and distortion at its widest focal length. Vignetting can be a matter of taste and left in, while distortion will require a bit of post-production work to fix.
Looking at images of brick and white walls is boring, so here's a real-world example of the X10's image distortion and vignetting. Shot at the widest focal length and aperture settings of 28mm and f/2 respectively, you can see vignetting around the edges as well as a slight warping of the plate in the center of the image.
The X10's images are generally clear and sharp. Oddly, diffraction seems to set in early, as the X10's edge to edge clarity appears sharpest from f/2-f/5. Still, we believe most won't notice as long as they're not viewing the images at 100%. Image distortion at the widest focal lengths is more apparent, and will need to be fixed in post-production.
The X10 produces noticeable vignetting (dark edges) from f/2 to f/2.8. Vignetting clears up around f/5.6. We don't mind a little vignetting ourselves, but it's a matter of personal taste, as it will alter the aesthetics of your image.
The X10 has an imaging issue you should be aware of. Under certain lighting conditions, artifacts which look like white orbs can sometimes be seen. They seem to appear when shooting into light sources or into strong highlights in low light. We haven't seen them appear under natural light or indoor lighting while not shooting into any light sources. Fujifilm has released a firmware update 1.03 to resolve the problem, but it appears that the firmware does not change much. The problem also seems to vary from set to set.