A reader just tipped us off to the iPhone 2.0.1 update being out RIGHT NOW. Just fire up your iTunes and click the old update button and you'll be able to grab it. We're updating now and will let you know what's different. Right now all we see is "Bug Fixes" listed under the changelog, but there's a security update info link in the update screen as well, so it might be that. [Thanks tipster!]
Update: It's an E. Honda-like 249MB, so this will take a few minutes to download.
Update 2: iPod Touch users can also update.