I really don't know what to say about this one. The Auto Downloads feature has been in the Dashboard over the last few updates, originally in the Xbox Live Arcade section, now in the new Games Library.
The way it was supposed to work is that once you were in the Arcade (and I guess now in the Games Library?), new trials of Arcade Games would automatically start downloading from the Marketplace. So let's say on Wednesday morning you could go into the Arcade, and new trials would get queued for download.
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