Littlefinger is supposed to be off at the Vale wooing Catelyn's sister. But we know he's not really there, at least at the time of the wedding, since he's on a boat at King's Landing waiting for the fool to bring Sansa to him. There is nothing in the TV series that seems inconsistent with this. He'll probably show up in the next episode.
The one interesting thing about Shae in the TV series is that, at the pre-wedding lunch, Tywin tells Cersei to "have her brought to the Tower of the Hand before the wedding". That makes me think he will somehow interfere with her leaving King's Landing, and bring the storyline back to where it should be in the books. If Tyrion thinks she's gone from King's Landing, and then sees her in Tywin's quarters during the prison escape, that would make for a powerful scene.
Another interesting change from the books -- Sansa is given a necklace by the fool instead of a hair net, but it seems it still played a role in Joffrey's death. In the scene in the TV show where Lady Olenna walks up to Sansa at the wedding feast, they show her fondle Sansa's necklace, removing one of the jewels. You can see the necklace with the missing jewel multiple times after that. But they don't show how it gets into Joffrey's cup.