I ran AdAware and Spybot S&D, came up clean. This is happening just recently, and while not a huge deal, it’s kind of irritating.
When opening new browser tabs in IE7 (7.0.5730.11) using the center mouse button, the new tab opens, but IE loses focus altogether. I don’t know where focus goes – even when nothing else is running, IE just loses focus. I have to click back into the page to regain focus (and, thusly, scroll mouse functionality).