If you happen to be running a machine with the following wireless card (i.e. those of you with Toshiba Satellite laptops), be sure you read the details before updating;
Atheros AR5007EG Wireless Network Adapter
I've just had an update available for this via Windows Update, and whilst it mentioned a restart would be required (though this information was ONLY available in the extended details, which I rarely read), it did not mention that it would wipe out any saved networks, which meant I had to reconfigure them - oh joy.
If you install this update and DO NOT restart the machine, you may notice Windows telling you the adapter does not match the requirements of the wireless network - this is completely untrue. Just reboot your machine and all will be well again.
If anyone from Microsoft is reading this, this update requires a restart, so have Windows Update ask if it can restart after installing the update. Don't rely on the user reading the details - most don't bother. Oh and, ensure it doesn't wipe out any saved wireless network configs ;o)