Bruno,
Synchronicity! I just came across them yesterday myself and was going to add it to our Smartermail Anti-Spam Checks before our annual Anti-Spam Effectiveness Audit.
It's pretty easy to add to Smartermail:
SECURITY > ANTI-SPAM ADMINISTRATION > NEW RBL
Name: Protected Sky - Yellow
Description: http://psky.me
Weight: 10
Hostname: bad.psky.me
Required Lookup Value: 127.0.0.2 Enabled: On
Enable for Filtering
Name: Protected Sky - Red
Description: http://psky.me
Weight: 30
Hostname: bad.psky.me
Required Lookup Value: 127.0.0.3 Enabled: On
Enable for Filtering and SMTP Blocking
So far they are really responsive (< 20ms), although it won't be until the end of next week before I can verify what kind of effective percentage each of these catch, but any new tool in the arsenal is a welcome tool.