[moz]

Offset printing runs ~100-300lpi depending largely on the paper used. Newsprint can go as low as 50lpi but it starts to look really bad (for stuff like posters rather than things you're supposed to look at). Serious glossy magazines (art mostly) can go over 600 lpi but that's rare (and expensive).

If you're looking at printers, 300dpi is reasonable, 600dpi is about as high as makes any difference unless you're using really high grade paper and are fanatical about halftoning gradations. But on common "printer paper" it takes a bit of experience to see much value past 300dpi - most people can tell the difference if you give them two pages side by side, but give them one page and they have no chance at guessing the print resolution.

Also, for black text on white paper, 300 dpi is ample. It's really only for pictures that higher resolutions make any difference, and that's where dot size/intensity control starts to be really, really important. A dot printer (dye sub, bubblejet) that has (say) 16 dot sizes at 300dpi can walk all over a "1200dpi" printer with a single dot size (common in cheap models), especially if its ink control is not very good (so the dot size varies but not under control of the printer).

Personally, 300 ppi at 16 gray levels would be fine for me. I'd rather see more contrast (and contrast control) than more pixels once we get to 300dpi. One thing is that there's almost certainly s a tradeoff there - more pixels means more dead space compared to pixels, so the effective contrast will drop. LCD displays and digital camera sensors have this problem, for instance.