As someone in a similar position, let me tell you my reasoning for getting the 3100 instead of the 3000.
From what I have read, the 3100 is a bit faster than the 3000. Nothing huge, but Japanese users who have both have commented on it. The 3100 has more internal flash, which can't be a bad thing. I believe that this is part of the reason that the 3100 is faster, too, since none of the OS resides on the microdrive (correct me if I'm wrong). This also means that replacing the microdrive with compact flash on a 3100 probably won't result in the same kind of speed improvements seen with a 3000 (so you might be better off getting the 3100 and saving the money you'd have spent on the 4GB CF).
Also, it's a better color (not black, but more like a charcoal grey). I don't know how this will affect you living in Austria, but the 3100 also comes with a charger that can be used in the US directly, as opposed to the 3000 which needed a different charger. Given that the price difference isn't that huge, and given the fact that the 3100 probably has other minor improvements that we aren't aware of, it seems to make sense to get the newer model.
I'm hoping that Sharp will release a new model sometime soon as well, but the 3100 really just came out a few weeks ago, so I don't expect it really soon. And who's to say that it will definitely include wi-fi? Everyone sort of assumed that the successor to the 3000 would include it, but it didn't.
