As mentioned it's going to be a crap-shoot. I've demoed all the cams in the prosumer class, including the GRDIII after purchasing my EX1.
I certainly would not buy an X10 without a demo. I've been trying to get info about it and Fuji DE has been extremely evasive about it.
On paper much of it looks fantastic and I'm very optimistic, though the leaks so far are not terribly promising. However, we're going to have to wait for real pictures and also for the S100 and real pictures from it as well.
If you choose to go with the others in the prosumer class, luckily, they are all quite good, with different strengths and weaknesses. I would also not count out the EX1, unless you absolutely care about video. Despite certain drawbacks (firmware and lack of Samsung response to anything), I would not count it out. One of the things I like about Canon and Panasonic and Ricoh is finer adjustment of the ISO rating, important for balancing noise vs shutter and sensitivity on cams like this.
Basically, wait, and don't buy the X10 without an extensive demo, especially after what happened with the X100.
Examples of my (mostly EX1) photos:
doctormorbid's photosets on Flickr