The new Nexus 7 is a sweet device, but it's not uncommon for a new product to have a few bugs. Such is the case with the NN7, which was exhibiting odd touchscreen behavior for some users. Google has confirmed that an Android 4.3 update with a fix for the touchscreen bug is going out now. Indeed, build number JSS15Q is starting to hit devices right now.
Some users in the Google products forum are reporting that the update does alleviate their touchscreen woes. The new Nexus 7 has also been reportedly suffering from some GPS issues, but there's no word on whether or not this update has anything to do with that issue. There might be other changes too, but we're not yet sure.
You can start obsessively tapping the update button in the system settings, but give it some time. As with all updates, the URL for the OTA file will probably be spotted by someone, which will allow you to manually update.