There are a few people who own the S2 Pro or S3 Pro cameras and can produce beautiful pictures from them. Witness is one of them.
As for comparing, there really isn't a point. The Fujifilm dSLRs stand in a class of their own. Unless you are going to spend brain cells crying over the technical specs of the body, it will be far more productive to compare the output capabilities of each. That said, only a handful of people who've used the different systems will be able to answer that. And even then, it'd be a never-ending argument.
If you are an ordinary shoot-nice-pictures-to-keep non-professional, pick whatever suits your budget and your habits. I won't recommend the Fujis even though I'm a Fuji user. The cameras take a lot of getting used to. And a fact is - there are quite a few S3 Pro users around who'd embarrass the technology (hehe... I'm sure one of them's reading and will MSN me to complain soon...) within.
As for the full-frame argument, I'm sure there was an early prototype S3 Pro that was built as a full frame, so that kind of stuff isn't far from reality. The issues are more likely to centre around light fall with the lenses rather than with the sensor size, Fujifilm has had full frame sensors since a long time ago.
* sorry, major typo error *