I can't stand that 'Put Your Hands Up!', harsh flash look. Like nippa, I prefer available light as well.
Having said that, I own an X10 and X-S1, along with the EF-20 and EF-42 flashes, and the flash integration on these things is wonderful. In the camera menus, there is a separate menu item that allows you to increase flash exposure +/- 2/3 of an f-stop, which applies to the onboard as well as any Fuji dedicated flash. As well, the 20 and 42 allow this sort of thing from their back panel as well. This is separate from the non-flash exposure compensation as well. Both the 20 and 42 allow bounce angles, and the 42 swivels as well: Very handy if you throw the camera up on one end, as you can still use it for bounce flash.
I'd like to get the EFX-20 later for its look on the camera, but it does not bounce.
Incientally, I run both of mine on rechargeable AA's, and would never go back to alkalines: Faster recycles for longer periods, and you keep your money !
I'd definitely agree with nippa. I'm not a 'flash guy', but these things have added quite a bit to my photography as they're just so effortlessly good.