Likewise; sorry for the delayed response.
However some of my clients freak out when they receive any SPAM even in their Junk folder. I guess its to be expected and that is all part of helping them understand.
Yes; this is a user education issue. I've had users insist that "really spammy spam" be deleted automatically, and then the same users throw a fit when a "super, ultra important" message is deleted automatically and unrecoverable. Your users will hate you either way.
Yes, it seems that we have very similarly-configured systems. You should be able to follow the same instructions for using Antispam that I did.
Regarding the Dovecot Antispam plug-in, there is complex and convoluted history behind the source code that makes downloading, installing, and configuring the plug-in quite difficult -- unless you know which questions to ask.
Which version of the plug-in you install, and which installation instructions you use, depend entirely on which version of Dovecot you use (v1 vs. v2).
I am using Ubuntu 10.04 (until 12.04 is well-vetted), so I'm stuck with an obsoleted version of Dovecot (1.2.9). This version of Dovecot requires the version 1 ("Johannes") plug-in, whereas Dovecot 2 requires the version 2 ("Eugene") plug-in. (Johannes developed v1, and Eugene took-over with v2.)
There's a lot of useful information in a thread that I started on the Dovecot mailing list, regarding this very issue:
That thread contains everything you could possibly need to install the plug-in and get it up-and-running.
That said, feel free to reply with any questions if you get stuck.
Finally, regarding the Extending Perfect Server tutorial, I have not followed it myself, although, upon a cursory review, I have taken most of the measures outlined therein on my systems. Overall, that tutorial is unrelated to Dovecot + Antispam plug-in, and I don't see any issues there.
If you are asking whether or not you should complete some or all of that tutorial, in general, I would say, "Yes, but not blindly." For example, there are aspects of that tutorial that no longer apply (because the affected software has been patched in a future release, for example), and following those steps will actually break software that may have been working without issue previously.
Unless you are an expert, you run the risk of creating more problems than you solve.