I use it since a long time, so since it works pretty good for me, I want to share how to handle the spam for your @gentoo.org address with procmail.
First, you need to say that procmail will filter your email(s):
echo "| /usr/bin/procmail" > /home/${USER}/.forward
Then create a simple /home/${USER}/.procmailrc with this content:
:0:
* ^X-Spam-Status: Yes
/dev/null
:0:
* ^X-Spam-Level: \*\*\*
/dev/null/
:0:
* ! ^List-Id
* ^X-Spam-Level: \*\*
/dev/null/
:0:
* ^Subject:.*viagra*
/dev/null
:0:
* ^Subject:.*cialis*
/dev/null
:0:
* ^Subject:.*money*
/dev/null
:0:
* ^Subject:.*rolex*
/dev/null
:0:
* ^Subject:.*scount*
/dev/null
:0:
* ^Subject:.*Viagra*
/dev/null
:0:
* ^Subject:.*Cialis*
/dev/null
:0:
* ^Subject:.*Marketing*
/dev/null
:0:
* ^Subject:.*marketing*
/dev/null
:0:
* ^Subject:.*Money*
/dev/null
:0:
* ^Subject:.*Rolex*
/dev/null
:0:
* ^Subject:.*Scount*
/dev/null
:0:
* ^Subject:.*glxgug*
/dev/null
:0:
* ^Subject:.*offizielle sieger*
/dev/null
:0:
* ^Subject:.*educational*
/dev/null
:0 B:
* $ content-[^:]+:${WS}*.+(\<)*(file)?name${WS}*=${WS}*\/.+\.(pif|scr|com|cpl|vbs|mim|hqx|bhx|uue|uu|b64)\"?$
/dev/null
:0 B:
* ^Content-Type: .*;$[ ]*(file)?name=\"?.*\.(pif|scr|com|cpl|vbs)\"?$
/dev/null
:0 B:
* ^Content-Type: .*; [ ]*(file)?name=\"?.*\.(pif|scr|com|cpl|vbs)\"?$
/dev/null
With the filter for X-Spam-Status and X-Spam-Level you will avoid the majority of the incoming spam.
Some mails that does not have any Spam flag, contains subject like viagra, cialis ( which I absolutely don’t need 
), rolex and scount.
Yes, I could you the (c|C)ase syntax, but I had problems, so I prefer to write twice the rules instead of have any sort of troubles.
Note: with this email address I’m not subscribed to any newsletter or any sort of offers/catalogs so I filtered scount, markerting, money.
Sometimes I receive mails from people that are not spammer, with the X-Spam-Level flag with one star, so I decided to move these email into a folder, they will be double-checked with naked eye:
:0:
* ^X-Spam-Level: \*
/home/ago/.maildir/.INBOX.pspam/
To avoid confusion I always prefer to use a complete path here.
After a stabilization you will always see the annoying mail from the bugzilla which contains ${arch} stable, so if you want to drop them:
:0 B
* ^*(alpha|amd64|arm|hppa|ia64|m68k|ppc|ppc64|s390|sh|sparc|x86) stable*
/dev/null
Now, if you are using more email clients, on more computers, you may need to set the filters here instead of on all clients you are using, so for example:
:0
* ^From.*bugzilla-daemon@gentoo.org
* ^TO.*amd64@gentoo.org
/home/ago/.maildir/.INBOX.amd64/
And so on….
These, hints obviously are valid on all postfix-based mailserver; if you are using e.g. qmail, you need to move the .procmailrc, but this is still valid.
I hope this will help 
EDIT:
If you need a particular set of rules, you can write it if you take a look at the source/header of the message, so If for example I don’t like to see the mails from bugzilla of the bugs that I reported:
the header says: X-Bugzilla-Reporter: ago@gentoo.org
so:
:0
* ^From.*bugzilla-daemon@gentoo.org
* ^X-Bugzilla-Reporter.*ago@gentoo.org
/dev/null