What exactly is better about this one than Akismet?
I would personally love to see 2 things:
1) the ability to report BACK to their service, which is something I do not think we can do from s9y antispam to akismet, and
2) a mention of s9y on their site... they mention Moveable Type, TypePad and Wordpress... its time to start getting Serendipity mentioned in some of these services!!!