Doesn't look bad from here, but then we're looking at small images on a screen - what you see on a print can be different. A little sharpening and it would probably be fine in an 8x10 - even the cropped one.

The flash is a little bright though. The SB800 is one option, but dialing in some flash compensation would probably help. When I use fill flash, my starting point is to put the flash at -1.0. That brings the subject out without a "flashed" look. Keeping up with all of the latest technology is pretty tough. You can probably experiment with your SB50DX and get different results from it - one thing I'm usually doing on my DSLR is shooting my SB28's (old, non-DX which doesn't work with Fuji anyway) is using good-old-fashioned "A" mode. That uses the sensor in the flash instead of TTL. It's working pretty well for me, but I know the latest stuff like the D2H or D70 with the SB800 is supposed to be almost as good as it was with film cameras.