To address part of your question, the iPad is far more than a toy for mathematicians, especially for reading mathematical articles. Goodreader is the best means of reading and annotating PDFs I’ve ever seen; in particular, the usual size of LaTeX articles fits very well on the screen, with a little zooming, even in portrait mode. I’ve virtually eliminated my use of my printer, both for reading others’ articles and correcting my own XeLaTeX output.
Be very sure to test a PDF reader on real articles before it’s too late; even Adobe renders the Computer Modern font unacceptably on-screen, though with decidedly different results in different situations and platforms, and Okular on Linux is virtually unreadable at 100% zoom.
For note-taking, I’m not a big fan of raw handwritten text (disclaimer: I worked at Apple during the Newton days, and at Palm); I expected to have to buy a hardware keyboard for my iPad, but haven’t needed to yet.