For web surfing, gaming and media consumption (videos, music, books, etc.), the N7 works quite well and could certainly replace a laptop/desktop computer. It did for me. Adding a keyboard probably wouldn't enhance the media experience.
For very light productivity (simple documents and spreadsheets, very basic photo editing, etc.) and more intensive web browsing, the N7 is acceptable, but would probably be better with an external keyboard and mouse. A 10" tablet would be easier to use, however.
For heavier duty productivity (complex or large documents and spreadsheets; full fledged video, audio, and photo editing), I don't think the N7 or any tablet or netbook is appropriate. I would only recommend a standard laptop or desktop computer in these cases. Besides the inconvenience of the tablet form factor (regardless of keyboard availability), tablets lack full featured software, and sometimes horsepower, to deal with these tasks. The exception might be the upcoming Microsoft Surface Pro tablet with a keyboard, but for that money, I'd probably just buy an even more powerful laptop.