Applied Bayesian Filters uses
Spambayes e-mail filtering application to rate the 'spaminess' of a given website. You can even
submit sites to train the Bayesian filter or access the
rating service as an RPC
Right now the current rating for my blog is...
X-Spambayes-Classification: unsure; 0.50
... but it has only been trained on with a handful of sites so far so hopefully the classifications will be a bit more discerning later.