Below is a snapshot of the ruleset that the extension author uses. It is commented to show the concepts it makes use of.

Please note that while this is a wonderful set of rules, it is aggressive. It's very possible, as is evident from the 'positive karma' rules, for important things to be blocked. Although this is a valuable starting point, it's still intended that users of this extension understand the ruleset and know how to maintain it (or at least disable the blocking altogether, when something seems wrong).

[Settings]
threshold=50
cutoff=75

[Inject]
function='AdWriter'
function='htmlAdWH'
function='urchinTracker'

# These are, more or less, false-positives that are caught below.
# Note the use of the "\b" word boundary regex.
[Group]
name="Positive karma, keywords"
score=-36
rule=$url=~'(downlo|uplo|thre|typep)ads?\b'
rule=$url=~'\bad(don|min)'
rule=$url=~'\bminify\.php\b'

# "Third party" hosts earn karma below.  These are hosts that
# are either unlikely to be malicious and/or critical to the
# functioning of common sites.
[Group]
name="Positive karma, hosts"
score=-36
rule=$url.host=~'static'
rule=$url.host=~'\.(aolcdn|files\.wordpress|gawker|yahooapis|yt?img)\.com$'
rule=$url.host=~'\.(akamai)\.net$'
rule=$origin=~'newegg.com/'

# Positive for flash, because blocking any part of a SWF
# makes the entire thing disappear.
[Group]
name="Positive karma, flash"
score=-75
rule=$origin.tag=='EMBED'
rule=$origin.tag=='OBJECT'

[Group]
name="Positive karma, google services"
match=all
score=-50
rule=$url.host$='.google.com'
rule=$url.path=~'/(account|adsense/login|jsapi|maps|uds)'

# The "third party" script in the RSS viewer tends to get blocked.
[Group]
name="Positive karma, browser chrome"
score=-1
rule=$url^='chrome://browser/'

# Now the "bad" scores start accumulating:

# Any third party resource earns some bad karma.  Not enough
# to get blocked, but enough to tip the scales.
[Group]
name="Third-party"
score=30
rule=$thirdParty==true

# Same goes for all javascript.  30+20 means all third party
# scripts are blocked, unless matched above by a "positive" rule.
# This blocks almost all trackers and ads.
[Group]
name="Scripts"
score=20
rule=$type==script

# Adding karma for iframes, as well as scripts, blocks almost
# all the rest of the ads.
[Group]
name="IFRAMEs"
score=40
rule=$origin.tag=='IFRAME'

# Now we start matching keywords, for things that haven't already
# been blocked.
[Group]
name="Keyword: ad"
score=35
rule=$url=~'\bad'
rule=$url=~'ad(s|vertising)?\b'

[Group]
name="Keyword: banner"
score=25
rule=$url=~'\bbanner'
rule=$url=~'banners?\b'

# Images earn just a smidgeon of negative karma.  They
# are sometimes used as the "lazy third party" transmission
# mechanism.
[Group]
name="Images"
score=10
rule=$type==image

# The longer the URL, the more likely it is transmitting all
# sorts of data.  Web trackers commonly do this.
[Group]
name="Long URLs"
score=10
rule=$url.path=~'.{125,}'

[Group]
name="Extra-long URLs"
score=10
rule=$url.path=~'.{275,}'

# Annoying images inserted into feeds.
[Group]
name="Feedburner/Wordpress cruft"
score=15
rule=$url.path=~'^/~./'
rule=$url^='http://feeds.wordpress.com/1.0/'

# Geocities ads.
[Group]
name="Misc"
score=30
rule=$url.path^='/js_source'