Calls to TileUpdater.GetScheduledTileNotifications appear to result in allocations in the Runtime Broker process that never get reclaimed. The size of the allocation appears to be influenced by the number of scheduled tiles, so applications with few scheduled tiles would cause the Runtime Broker to leak slowly. For applications with many scheduled tiles, however, the allocations are quite large and can result in several gigabytes being allocated if the method is called frequently, such as in background tasks.
This is a very real problem. I have one of the clock applications in the Windows Store and I was using this method to determine how many updates were scheduled so I could top off the queue with more. After a couple days in the store, people started reporting huge memory leaks in the Runtime Broker -- several GB. Web forums are filling up with people complaining about this leak and associating it with my app -- even though I'm now getting email from people complaining about the leak and they don't even have my app installed. As more apps come online in the Store this is only going to get worse.