I've had the Nikon E68 Wide Angle Converter for a few days now and am post my first impressions. There is plenty of info on this already, but hopefully you find this helpful. Enjoy!
I love the x100 but I also sometime enjoy shooting at wider angles. I didn't feel like waiting for the official fuji wide angle converter or feel like paying the high price of admissions for it. So I went with the Nikon E68. I got it from ebay for 59 bucks! Below are my quick amateur/non-pro feelings and comments about it and a few of my first shots with it.
-Setup: x100 + hoya filter + step down converter (so the E68 can fit the x100) + Nikon E68
-Build quality: it's definitely a nice hunk of metal and grass and also threads on nicely. definitely getting your
-Handling: it fits on very nicely on the x100. it does make the camera a bit heavier but also makes the x100 nicer to handle since you can hold the barrel like you would with an slr.
-Performance: the converter gives usable photos starting at aperture 5.6. anything below that and the images are too soft. but it gets sharper above 5.6. the images tend to be sharp at the center but get soft at the edges. distortion doesn't seem to be too bad. i've been shooting with the fuji wide angle setting set to on which seems to help a tad. also, the converter flares out at the end and cuts off some of the light coming from the flash. so depending on the situation, you may or may not want to use the flash.
-Overall: for an entry fee of 59 bucks it gets the job done for those that sometimes needs a wider angle on the x100. the lens does have it's limitations and will probably most be useful when shooting in bright light since you have to stop it down to get sharper images. below are a few sample shots (images are the jpegs straight out of the camera). thanks!
With and without the E68: