I have connected the mail app from the galaxy s2 to my email (exchange). The notification (which I have set to vibrate) is just a very short vibrate. It seems very likely that I will often miss this notification (unlike the gmail app for example which vibrates for a much longer time). Is it normal for the vibration of the default mail app to be very short? And if so, is there a way to change that?

There are two methods you can use to adjust the vibration duration:

System Configuration

1. Tap your device "home" button;
2. Tap your device "menu" button;
3. Tap "Settings";
4. Tap "Sound";
5. Use "Vibration Intensity" to adjust the duration.

^{This may not be available for all devices/Android versions}

Custom Application

There are a few applications available from Google Play Store that you can use to adjust vibration timers.

Vibration Notifier by j4velin allows you to set a vibrate interval and additionally alows you to specify the duration of each vibration:

Let your device vibrate every X min. when you missed a call / received an eMail