I am an unabashed fan of the Yarn Harlot. Recently, she received a new scale, so (copycat that I am) I bought one for myself. Mine (from Target) is not nearly as cool as hers, but now that I have it, I wonder why a scale is not a requirement for all knitters. It immediately relieves that am-I-going-to-run-out-of-yarn angst and answers the eternal are-we-done-yet question.
For example, I am knitting a sock from a skein that is supposed to contain all the yarn that is needed to create two socks, but the skein seems to be shrinking too quickly. Plop the skein on the scale, though, and I can see that the almost-done sock has used 40 grams of a 100 gram skein. Or when will the 4-color baby blanket be done? I plan to end the blanket when I use up the melon, as it is the color that will run out first. I weigh the ball, knit a row, weigh the ball again, and voila, I see that I have enough yarn to repeat the 12-row pattern three more times.
This is the perfect gift for the anal retentive in your life!