Updates
Updates are almost as important as the initial purchase of the app itself. Updates can provide crucial bug fixes as well as new features.
Intel AppUp
AppUp has an Updates pane in the My Apps tab which lists all the available updates for your downloaded apps. Simply click on the button beside each app to update it. None of the apps we downloaded had any updates available at the time of writing so we can't say for certain how well this works, but we don't anticipate any problems.
We're still waiting for confirmation from Intel on whether developers can offer paid upgrades with discounts for existing customers, as they can with traditionally-sold software.
Mac App Store
The Mac App Store has an Updates tab that lists which of your installed apps have updates available. Clicking the button installs the update a process which looks identical to purchasing a new app. Apple's rules specifically prohibit apps from using their own separate updating systems, so all updates will take place through the App Store. If you keep the App Store's icon in your Dock, it will automatically update to show the number of available updates which is useful visual reminder.
If you already own an app sold through the App Store, it should appear marked as 'Installed' in the store so you don't accidentally purchase the app again. In our experience however, while our pre-existing copies of Apple's iLife apps were correctly recognised, our copies of Apple's iWork apps weren't. Unfortunately, pre-existing apps can't be updated through the Store unless you purchase them again.
We're also awaiting comment from Apple as to whether developers can offer paid upgrades with discounts for existing customers. Since this isn't possible on the iPhone App Store, we're not holding our breath.
Winner: Tie. Neither AppUp nor the Mac App Store are perfect when it comes to updates. Both have room for improvement. The approval processes on each app store could delay the availability of important updates though.
