Blocks blog spam
A script installed on your site relays posts to central Sblam! server for analysis and gives you the results.
It's up to you how spams are handled. Sblam! has very high accuracy (99.8%) and reports when it's not certain about the result, so you can manually judge toughest cases.
Yes. It does work with any PHP-based site which uses standard POST forms, but you have to integrate the filter yourself. Wallace has written a simple WordPress plug-in (plug-ins for other CMSes are welcome).
Posts sent to Sblam! server are stored and read indeed, but please keep in mind that these are posts which you intended to publish on the Internet anwyay.
Cookies (except a single one which is private to Sblam!) are not sent. You can keep some form fields secret by unsetting them with
Links to this site from Sblam!-protected pages are welcome (but not required).