Like Tomaž I had to deal with a flood of comments lately, sadly mostly spam and they are simply taking too much time to clean up. I think I could catch most of them by sending whole comment to Google search, parsing response for excerpts and match for similarity.
Regretfully I don’t have time to build this and it wouldn’t scale (I’m curious why Akismet doesn’t do something like that). So following Tomaž’s research my plan is to turn off comments until botnet learns comments here don’t work and then turn them back on. This shouldn’t take more than a couple of weeks.
Until then you will need an account to comment which anyone is free to create (for now). Sorry.