I think BeckAndCall's caution is right about the extra-curricular side. Obviously many of our students are multi-talented, hugely energetic and motivated and have lots of other interests - the university is full of societies and activities. BUT, for admissions, extra-curricular interests are not really of much interest to us.
If you think about it from a tutor's perspective, I want to find someone to whom I can give a reading list one week, and know that they will be able to dedicate themselves to the work, without much intervention by me. Then come back the following week with a 2,000 word essay.
Therefore, we are looking for candidates really dedicated to (maybe obsessed by?) their subject and the process of studying and learning. Curiosity, and intellectual precision, and a kind of ceaseless desire to carry on finding out about a subject are what we want. If candidates are too well-rounded, and have too much of their time filled with scheduled activities, then it's harder to be confident that they will be the sort of autodidact our system needs.
This is not to put anyone off their extra-curricular activities at all. As posters have said, activities which complement their intended subject are great. But academic achievement and potential are much more important in our admissions system. We do know that other universities want to see details of extra-curriculars on personal statements, however, and read that paragraph of the PS very tolerantly!