I don't know what I did, but recently when I opened Microsoft Word document, I experienced very slow app switch between it and other applications. When I start Word in Word's safe mode (as described here http://wordprocessing.about.com/od/troubleshootin1/qt/safemode.htm ), the issue disappears. Now I don't know where to find out which plugins were loaded that's causing the problem. Or where the normal.dot is if that's the problem. I'm on Windows 7 64 bit. Thanks.
EDIT: I'm using Office 2007.