Google has been in a cleaning spree in recent years, as they've decided to focus on successful projects and experiments and kill off the less popular, less efficient, or less profitable ventures. They call it "spring cleaning" no matter what the time of year. Fans of axed products are also sure to grumble no matter the time of year. Here's what got killed at the end of 2012.
Google Calendar features
As of January 4th, these features are no longer available for new events (they'll still work for old events). Appointment Slots, Calendar Labs Smart Rescheduler, checking calendars via SMS, and creating events via SMS.
Ok, SMS calendar manipulation is just inefficient these days. There may be a few grumblers, but this is clearly a dying feature that drains Google support. Get a smart phone if you need to check your calendar from your phone, and use an app. People using the Calendar Labs Smart Rescheduler can use the Find a time view or Suggested times, so they're not completely out of alternatives.
The loss of Appointment Slots is a real bummer. It was a very useful feature, but few people knew it existed or how to use it. Pity. This is something I use and teach other educators to use, but I suspect we're one of the few subgroups who were fans. Basically this allowed you to set up slots that were visible to others as available times. The viewers (say, your Comp 101 class or your Swedish massage clients) could then pick a time for an appointment. It would show up to viewers as unavailable without specifying who had singed up for the slot, but you (the person who created the calendar event) could see who booked an appointment.
Remember when you could use this feature to sync your Gmail, Google Calendar, and Google Contacts with your Microsoft Exchange account? Yeah, well now you'll have to do it differently if you don't have Google Sync set up already. Google is killing off the Google Sync service. They're adding CardDAV (an open format for contact syncing) support to the existing IMAP (email) and CalDAV (calendar) support, which means iPhone users can cobble together a way to keep it all in sync without paying Microsoft a bunch of money to sync through the protocols that Microsoft uses and that dominate in the business world. Speaking of the business world, Google Apps customers can still use Google Sync, but since Google killed off the free Google Apps accounts, Google Apps users are mostly paying for the privilege. (Google Apps has a free educational version of the product, but the strategy there would seem to be to offer Microsoft syncing support in the hopes that schools would be enticed to switch over to a cheaper, fully Google-run email system.)
Syncing also went away for Google Calendar and Google Sync for Nokia S60, and the SyncML (which was used by old mobile devices - maybe it's time to upgrade your phone, guys).
If you've already got a Google Sync setup, you're fine. It won't end. It's just the ability to set up new syncing that will go away. They removed the link to download the client. The Nokia and SyncML service, however, are totally ending at the end of January 2013. Buy a new phone or use a third party app.
Google is also shutting down the Issue Tracker Data API, which is only of concern to people who host projects on Google Code. Nobody else is affected.
Punchd was a loyalty card app for smartphones that Google purchased a year ago. They're shutting down the service, and you've got until June 7th to use any remaining loyalty points. The engineering behind Punchd has already been integrated into other services, like Google Offers.