UPDATE: This has been addressed in iOS 5 with the introduction of the iOS Notification Center preferences. You can now disable alerts for Calendars in general!
I've searched high and low for a way to disable Calendar alerts on my iPad but have come up empty handed. So, time for a new post!
There doesn't seem to be a way to disable these alerts. You can disable the alert sound (through Settings → General → Sounds) but you will still get an alert window to remind you of the same event that you were just reminded of on your computer and iPhone.
Observed in iOS 4.3.1 (and presumably, every version prior).