I agree with most comments here, I feel that the bros didn't need to go into that amount of sexual detail just to show the relationship between neo and trinity. We aren't that thick, we can all work out that they are in love without having that scene shoved in our faces.
However, the cake scene. While i don't think that scene was absolutely necessary, as it was a bit lude, when i came out of the movie i thought to myself, "now there must have been a reason to put that scene in the movie". And there was. The Merovingian is showing neo how far he can go in the matrix, in terms of manipulating the code. Neo see's this and this is how he is able to save trinity at the end of the movie. In the first movie, neo finds out that he can rewrite the program. However, here he learns that he can rewrite how "people" are written. Essentially, what he and the Merovingian do are exactly the same.