Yes I also use my MacBook as my only computer. It's just easier, to have all emails and documents on just one computer. This way I can create something at college, work on it on the train back home and at home I can keep up where I left.
I upgraded the HD to 320 GB, so I have just enough storage space for all my music, photos and documents.
I don't use an external monitor, the 13 inch screen is just right for everything I am doing. Except for programming a second display would be good. But I am not programming that much. And I rarely do anyting video related.