I'm running WP 3.0.1 with WP SlimStat 2.0.8.
After recently and thoroughly updating my WP installation, including the plugins and themes, I realized earlier today that links on my site with target="_blank" would no longer open in a new window or tab. I verified this with Firefox and IE. It seems pretty bizarre (the embedded links are correctly formed and work when that block is pulled into a barebones HTML file).
After ruling out the theme (used default) and all other plugins (disabled them) I finally disabled the WP-SlimStat plugin, and the problem disappeared. To be specific this problem only occurs when the SlimStat setting "Enable JS Tracking" is turned on. I'm not quite sure what the value of that setting is but it certainly has a very annoying side-effect right now.