I got it earlier this week. It's pretty thick and has a lof of nice features.
It has character information (like statistics for Syaoran, Sakura, Fai, etc), information about the worlds they've been in, an interview of CLAMP, a bonus chapter and poll results of Japanese fans. There's also a bit of fan art contributed by Japanese readers. There are 4 colored illustrations -- nothing new -- and lists of the merchandise available for the series.
Also, it only covers info up to v7 of the manga.