Calendar app Tempo has been updated to address an issue where no new users could sign in to use the service. The app has now has implemented a similar reservation system that that Mailbox iPhone email app implemented upon launch.
Contrary to Mailbox, since I got into the reservation system, I haven't moved one spot. Since the app grabbed so much attention last week, I haven't been able to get in and thought the new reservation system could improve things.
Sadly, getting into using the app has been a real problem and hope I can get to use it soon. In the meantime, I use Sunrise Calendar, which was released earlier today.