as mentioned, f-spot probably uses the camera preview embedded jpeg, it is normal that you can zoom to 1/1 (i use geeqie, it does the same thing): just try to look at a picture with a lot of sky, for instance (in general: smooth wide area gradient), and you will imediately notice you are looking at a very low quality (highly compressed) jpeg. i like that approach for previews though, it is very fast.
i also use ufraw, and am pretty happy with the results and interface. i also use it in batch mode quite often. btw, rawtherapy is not opensource (last time i checked, at least), this is the only reason i have been too lazy to give it a try so far (i prefer open software, for peace of mind).
one more note: what you see (the difference) is not only due to white ballance, but also to other settings of in-camera raw conversion. as you change them, the preview jpegs will change too (on the pentaxes, i could even get a monochrome preview, while shooting raw, which can come in handy, i didn't manage to do the same on the gx10 though, the menus are designed differently, sadly), so in short, keep in mind that every raw converter will display a different look by default, there are so many parameters to raw conversion, that it is safe to say that the contrast, colors, sharpness, in general, the overall look of the output of each raw converter will be unique (it is even so between dcraw and ufraw, eventhough ufraw uses dcraw behind the scenes), so don't be frustrated, just look around and see what works best for you. another option you seem to not have tried is digikam, a very capable (and, similarly to RT, and unlike ufraw, "all in one" piece of software), and raw studio (both are also dcraw-based, both look entirely different from eachother, from ufraw and from dcraw as far as output is concerned
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