Spam Getting Past All Plugins

I manage a self-hosted company blog that has been running for a little over a year and gets a solid amount of traffic. We used to use the Gatekeeper plugin for blocking spam, and didn’t get any spam most days. When we upgraded to WP 2.7, the plugin stopped working, and since then the amount of spam we get has skyrocketed.

We’ve tried just about every spam blocker plugin out there, including ReCaptcha, Bad Behavior, and Quiz, but the spam has continued to roll in completely unabated. Akismet catches most of it, but we’re still getting at least 75 spam comments a day, all of which look very robotic and uniform.

Does anyone know why all of these plugins that seem to work well for others didn’t make any dent at all in our spam? Is there some automated way that people could post spam comments automatically, bypassing our spam protection? Could it be a setting in our WP installation?

I’m at the end of my rope as to how to at least cut down a little bit on the spam, especially since it seems to get worse all the time, but none of the recommended plugins have made a difference so far. Any help or suggestions would be greatly appreciated!