System error when I disconnect USB power

I just started playing with my Arduino Duemilanove this week, so this might be a dumb question. I have the Arduino connected via USB power, and when I want to power it down, I disconnect the USB cable... A few times this has resulted in a major OSX error saying that I might shutdown/restart my computer. Is there a better way to power down the arduino or safely disconnect the USB cable?

A few times this has resulted in a major OSX error saying that I might shutdown/restart my computer

You really shouldn't see a stop message when disconnecting the Arduino. Which version of OS X do you have?
Have you installed the latest drivers from http://ftdichip.com/Drivers/VCP.htm ?

running leopard...
I don't think I've installed the drivers you listed. Are these necessary for running the arduino through usb?

You might have already had them installed in some way. A lot of serial-based USB peripherals are really FT232s at heart, so many manufacturers include bashed up versions of the driver.

I'd recommend you install the ones directly from FTDI.

(The FT232 is the USB interface chip on the Arduino, you can see it directly behind the USB connector.)

actually on second check, I think I installed the driver right when I got the Arduino.

I've used lots of FTDI devices (I think I have about 8 right now) and have never seen this. I have seen a warning when unplugging one when the port is in use (e.g. the Arduino serial monitor is open).

I second the recommendation of downloading the drivers directly from FTDI and reinstalling.

-j

that might be the problem... I'm not positive but I think the serial monitor was open when disconnecting the usb cable... I guess I should be more careful that this is not running. Will test this out soon...