To separate it out, as an actual honest answer, the thing I probably couldn't do without is OneNote.
If you warped me back in time and my 6100/60 or 840av (or even some Windows NT computer) was relevant and modern, the thing I'd miss most is almost certainly my daily notebook, that syncs to my handheld, my desktop, and my laptop over the Internet.
(Oh, that's another issue entirely -- modern connectivity may not be as great as we know it could be, but it's so much better than in the before-times.)
If you warped me back in time and my 6100/60 or 840av (or even some Windows NT computer) was relevant and modern, the thing I'd miss most is almost certainly my daily notebook, that syncs to my handheld, my desktop, and my laptop over the Internet.
(Oh, that's another issue entirely -- modern connectivity may not be as great as we know it could be, but it's so much better than in the before-times.)