If you need to check wether zbook has been updated, you can always check out the timestamp of when it was last uploaded. Use this url:
http://www.users.on.net/~hluc/myZaurus/book/As for changelog, it is a good idea, but too much work for me and I am very busy lately. I just finished a crazy 80 hour work week and also had to fly back and fro between three different cities. It's just too much for me to keep up with...
Anyway, as for the C1000, it is very similar to the C3000 and C3100, more similar to the C3100. The difference between the C3100 and C1000 is that there is an internal harddisk so there is more space available to the C3100 but otherwise, everything is the same, same software, same kernel version and drivers, etc... so really, the only technical difference is that there is no /hdd3