iPhone calendar alerts are not muted when vibrate switch is on I leave my iPhone in vibrate mode all the time.  The switch still works (when I switch it the iPhone shows the ringer on/off notice).

This morning it started alerting me for calendar alerts with both vibration and audible chimes. Note that I'm NOT talking about clock/timer alarms.

I've rebooted the iPhone, and it's still alerting me both ways.

What else should I check?
The calendar alert is something that you asked for so will not be suppressed by the Silent switch. According to the HIG the switch is supposed to indicate that you do not wish to hear unsolicited sounds such as incoming call ringtones.