I hate to be a "Me Too" but...Me Too!
Last night I installed zcs-4.0.5_GA_518.UBUNTU6 onto an existing Xbuntu 6.06 (I think, although I may have run apt-get update && apt-get upgrade since the initial install) box.
I also setup fetchmail and will probably implement RulesDuJour pretty soon.
I had no real errors to speak of.
One thing that I did confirm was that it will not run on an OLD p200 with 64 MB ram... but then that was no surprise

Once I finally installed it on a more modern system (still only 500MB ram though) I had no real problems. The only things tweaked by hand were my relay host and my domain name in a couple of postfix files. Outside of that I am good to go....except for the graphs and I think I just found a thread that includes a fix for them.
Overall I was very impressed with the installation and with the product so far. I am testing this version at home with fairly modest requirements ( a handful of users and 3 domains) but would really like to eventually roll a version out to some of our sites at work.
This is just another example of the great systems that can come from open source type software (not to mention the community of support that is available.).
Thank you;
James
PS If you want to know anything specific about my settings I would be happy to post the content of any files, etc...