This is one of the most useful "everyday tools" on my Linux desktop -- and it is steadily improving, as well :)
In addition, the well-written/-documented/-maintained sourcecode and a very responsive main author make this one of my favourite open source projects.
I'm really liking this tool, and am right now trying to move it to an OpenSuSE 11.1 install - initially I couldn't find it as a SuSE package - I had initially encountered Zim in a Debian "Etch" package list, installed it, and was trying it out.
Then I started using Zim via SSH to the Debian box [from the OpenSuSE box], forwarding the X connection over the SSH connection.
Now I've got a copy of /usr/bin/zim (a perl script, btw), the /usr/share/perl5/Zim directory [not used on OpenSuSE platform - using /usr/lib/perl5/site_perl/5.10.whatever/
In used YaST to install all the Perl Modules I could find in the list. Note that Zim itself is not listed in any of the repositories that I have.
I think I see why the package manager packages are important - the Perl library structure of the two machines is quite different, and is requiring translation of e.g. the include path used by the 'use' and 'require' statements.
Overall I like Zim a lot. It does have a few problems - notably some spontaneous conversions of lists of links to some sort of un-correctable "Verbatim" version of the Wiki source code - I want finer control of the link target names [relative paths for sibling links, for instance], and what I think of as "the CSS and HTML output".
I like the file structure model, and the ease of creating free-form knowledge bases with heavy cross-linking.
I'm planning to do some work on this app, and so will be trying to connect with the development team, etc. I expect this to become a much better known program, soon, since with some simplistic support at the system level, it could become a light-weight, powerful, incredibly intuitive interface to maintaining a text knowledge base either locally on the desktop, or remotely e.g. on a web server.