In the free version one of the main gripes was you only got alerted of events on the day they happened. For example, when the calendar alerted you of a birthday you'd have no time to send a card or buy a present. In the upgrade you can set the calendar to remind you of events up to five days in advance :
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However if you like to only know of events the day they happen, you can set the new alert system to do that too :
The 'Don't Remind me again today' option is for people who restart their computers several times a day. In the old version, you would be notified of events every time windows started, which some users found unnecessary.