You know, I've really turned my iPad in quite the productive little machine.
My 15" MacBook stays docked to a large external monitor at home and I take my iPad 3 with a Logitech Ultrathin Smart Cover to school. I use Word (and occasionally OneNote) to take notes during lectures or annotate professor supplied power points as they talk. I use Excel for iOS for some (very light) spreadsheet organization. I'm using PDF expert to read and annotate over 400 pages of PDFs for this terms classes. I've stopped printing PowerPoint slides and notes and simply consolidate them all into one large (50 to 200 page) PDF to study for exams. All my files stay in sync via Dropbox. I use Calendar and various Reminders lists to stay onto of my tasks and I stay on top of my emails throughout the day instead of letting them pile up until I'm home.
When I get home I pick up where I left off on my Mac to finish papers, work on my online class presentations, and work on my thesis (but I read the thesis PDFs and data on the iPad).
Together they make a pretty good team. My Mac is excellent for my heavy lifting tasks and my iPad works perfect as a light on-the-go device. The ability to use a keyboard in a more traditional laptop fashion when taking notes, but detach it into a more "book" like form factor for reading and annotating PDFs is a big help especially since some of my PDFs are rendered as one image so I can't highlight individual text on my Mac, but I can draw or freeform highlight on my iPad.