I used the x100 since it came out last year and found it to be the perfect travel camera (small, lightweight, great image quality). As soon as the XP1 was released I picked one up and while it is larger, it is a phenomenal camera. I love the image quality that it produces and after only a few firmware upgrades, it is noticeably improved. However, recently I picked up an M9 and find it and the XP1 to be a bit redundant so I'm looking to sell the XP1. As much as I love the image quality, I can't justify having both cameras. That said, I've become spoiled by ISO performance as the XP1 is absolutely ridiculous when compared to my M, x100, or 5D2.
For those complaining about how heavy/light it is, I don't think that's a bad thing. Makes it easy to carry around all day! Coming from Canon and using a 5D2, anything that's smaller/lighter is a joy to use/carry.
If anyone's interested in my XP1, let me know.