This is a great plug-in, with an almost 99% catch rate it keeps the spam away from your site. I also use a basic math question on comments which has also helped; it prevents the post from even being posted by automated scripts. Since I started using this last year it has prevented over 1,200 spam comments from being posted.
Ever since I started using the Akismet plugin for WordPress I rarely if ever get any spam. You can see from the chart below it has caught over 1,000 spam attempts. I also use the math question on the comment form so bots can’t just submit the form – that has also helped out a lot. The great thing about Akismet is it catches it when its a manual submission by some spammer. I have however found about 5 comments that were legitimate in the spam bucket. The chart below is generated by the Akismet Stats plugin in the WordPress dashboard.