Hi there,
There is a good discussion about that here:
1354-The-Power-Of-ZOOM-Fixing-CSS-Issues-In-Internet-Explorer.htm
I have found, myself, that Zoom is good for forcing IE to obey Alpha commands... naturally with later versions of IE, this is not as much a problem - so you could probably eliminate Zoom if you are not concerned about IE6. I am not sure about IE7 response... but it may be worth testing without Zoom.
The thing to keep in mind is that Zoom is ONLY recognized by IE - so naturally, standards based validation is going to not like the command.
Best regards,
Brian