How do you deal with spam?

Hi, how do you deal with spam? For now i've found akismet...ok, everybody know it... the cons is that they require to be payed, if it's not a single and personal blog.... obviously with a mu installation where there could be thousands of blogs it would be quite expensive (expecially at the startup where there are other expenses).
Then there is typepad which offer the api access for free, is it possible to use with the mu, with a single api key for all the blogs?
And finally there is BB, which i read somewhere in the forum that is the one who use(s/d) edublogs too... but in that post is written also that it got a lot of false-positive... is it still like that?
Any other alternative?

For now i'm thinking about recaptcha, to insert it at least in the blog registration and to hide emails.... for comments it would be quite annoying insert a captcha to insert a comment......... personally speaking i'd not comment in that blog