I'm not a High ISO person but I found this interesting:
"Based on samples we saw today that were captured with a prototype camera, the sensor really shines with low light shooting -- the X-Pro1 can produce usable 16-by-20-inch prints even at ISO 25,600, which is the maximum supported sensitivity. Identical images shot with the 5D Mark II showed significant noise in shadow areas, while the Sony Alpha A77 (NEX-7) produced an image that you certainly wouldn't want hanging on a wall. The playing field was much more even at ISO 6400, where all three cameras captured usable images -- noise was still visible on both the Canon and Sony cameras, though it was indistinguishable in the Fujifilm print. Again, all of these samples were provided by Fujifilm, and were not the result of independent testing."
From:
Fujifilm X-Pro1 interchangeable lens camera preview (video) -- Engadget
Even more interesting is the 14mm F1.4 which is going to be released later this year. Apparently there are an additional 6 lenses (some F4 zooms- yawn) that are planned to be released 2012-2013. This is a really serious product. Why do I have to wait.................