I am using the customer_save_after event in magento, and all is working fine apart from 1 annoying thing - it is always fired twice.
There are no other
Be careful with Jonathans solution, 'customer_save_observer_executed' stays in the session, so event will not be fired again in the browser session. So it's generally a bad idea, because it will not allow to register two or more customers in a row(actually, it will, but events will not be fired)
I suggest the following solution:
public function customerRegister(Varien_Event_Observer $observer)
{
$customer = $observer->getEvent()->getCustomer();
if (!$customer->getId())
return $this;
if(Mage::registry('customer_save_observer_executed_'.$customer->getId()))
return $this;
//your code goes here
Mage::register('customer_save_observer_executed_'.$customer->getId(),true);
}