Twice during the latter half of "The End of Time, Part 1," BBC America ran an advertisement for Part 2. And even though there were a lot of rapid-fire images that would have soared over the head of a casual viewer, at least one major plot development was spoiled to observant or long-time fans. Bad move, to be sure, and I grumped about it just now in 2MTL #90.
BBC America had to run some kind of ad for Part 2 during Part 1; it airs at a different time next week, and casual viewers need to know when to find it. It obviously should have been a spoiler-free version for during the show.
Keep in mind a couple of things, however. First of all, the million or so people who watched "The Waters of Mars" last week, most of whom likely came over to see EoTP1, are on the whole more casual viewers than your average Twitter-consuming Doctor Who fan. They might have missed the significance of the images completely. Also, even a niche channel like BBC America has an audience that dwarfs the number of fans who might acquire episodes through illegal downloads. At most, a statistically significant number of viewers might consider waiting a second day to grab the unedited, without-commercials iTunes version.
It's a blunder, but there have been worse.