Not many people know the following …
you can switch between the Vibrate and your Default notification profile (i.e. your last notification profile other than Vibrate) just by holding the # key while at the Home screen until the profile changes. If your BlackBerry is password protected you do not need to enter your password - just dismiss the password prompt if it is displayed by pressing the Escape key (ie. the key immediately to the right of the trackball) before holding the # key.
For example, let’s say you are going to a meeting and your current notification profile is set to Loud - you can quickly change to Vibrate so as not to annoy the other attendees just by holding the # key while at the Home screen.