Alright, I found a good [link:www.repairfaq.org/ELE/F_Car_Battery.html#CARBATTERY_022|Car Battery FAQ]

Here's what that FAQ says about checking alternator by disconnecting the battery:

15.6) Test the alternator by disconnecting the battery with the engine running.
A battery as like a voltage stabilizer or filter to the pulsating DC produced by the alternator. Disconnecting a battery while the engine is running can destroy the electronic components, e.g., computers, radio, stereo, alarm system, etc., or the charging system. [font color=red]Just say NO![/font] if anyone suggests this.

I have tested an alternator by disconnecting the battery. But, I have since learned that it's a bad idea. I know several people that have done it, and I've never heard of any damage as a result. But, I say, "better safe than sorry". The way I check an alternator now, is to simply check the voltage at the battery terminals while the engine is running. Should be around 14V (differs from car to car). Read that FAQ for more info on it. Also, read about parasitic drain (although we've covered about everything in this thread already).