Julia's motivations (*SPOILERS*)
Is this supposed to be about revenge? Well, if it was, then I don't understand why Julia picked Avice to take revenge upon. She didn't do anything to Julia. Taking revenge upon T-O-M or her husband, yes, but Avice? It wasn't her who cheated, it was Tom and/or her husband. She didn't steal them from Julia.
The way I see it, Julia used Avice for the sake of her own glory as an actress. I didn't see any real feelings involved in what Julia did, and I certainly didn't find the character likeable at all. I think her son was right when he said to her that she was always repeating the lines from her plays in her conversations with people -in fact, we see an example of this when he says the same thing to her best friend (was his name Archie?) and to Tom: "you are the only one with whom I can be myself, let's go on seeing each other", etc. All the time I saw a great diva of theatre, with an inflated ego, hurting because her pride had been hurt, but I didn't see any real feelings for other people, just herself.
I'm not even sure what was it that we were supposed to think of Julia. Are we supposed to feel sympathy for her, to like her? I know that I liked the characters of her husband and of Avice more than I did hers.