My latest one (and it has been with me since last November at least) is the part-time MA in Victorian Studies at Birkbeck college. I had always thought I would become a university lecturer and would spend my life writing books and studying them and writing about them. Then life decided otherwise - too much studying kills the thirst for knowledge, and I just wanted to try completely new things. I became obsessed with music. So I started writing about it instead.
But the thirst has come back. I've started thinking that it would be a good idea to go back to studying again, especially an era that has always, well, obsessed me. I even have an idea of what topics I'd like to look at if I ever went on to do a PhD. Only the - hopefully near - future - as well as the state of my finances - will tell me whether this is possible, but the obsession is here to stay.