The Android 3.2 update for the Verizon 3G (soon-to-be 4G) XOOM can be flashed right now, before it hits your device over-the-air.
If you've flashed a custom recovery (and gave up the warranty), you can find update instructions over at MDW - in this case, you don't need our instructions below. This option is good for those with unlocked bootloaders (though if you're rooted, it seems the only update option right now is to install a pre-rooted update which will wipe your device).
Stock Recovery - Unrooted, Locked Bootloader
However, if you decided that unlocking the bootloader is not worth voiding your warranty or simply don't feel comfortable unlocking, you can still install the update before Verizon decides to push it to you, using the stock recovery.