The recent Xbox Dashboard update included one easily overlooked minor change. When you play a trial of a game, that information no longer shows up in your play history. Now, when you look at the games you have played, those games (which cannot earn you achievements) are treated as though you had never played them.
As a side-effect, services built on top of the Xbox APIs no longer have access to this information either. So, my Xbox no longer counts these when it blogs - previously this would show up in the blog, and count as activity it could discuss and consider in the very simple AI. On the bright side, services tracking statistics can now get more accurate information on zero achievement cases, because that now means a purchased game with zero achievements can be distinguished from a simple trial game.
Minor point, but interesting how a small change like this can trickle through the API and affect a variety of third party services.