I've actually had this ink pad for awhile but Scrapbook.com is encouraging people to write more reviews. Grey (or gray) is a vital color for all sorts of reasons.
In generally greys receed, they drop back not unlike shadows; this optical peculiarity means that you can create depth without a lot of fancy tricks or techniques. Stamping a brocade background in black is very harsh, while Hickory Smoke is a bit softer and more of a background.
Grey is often a better way to darken a color. Adding black is hard to control, at least for me. Mixing a little grey in another color with a blending tool on a craft mat or palette gets better results.
Grey can also create all sorts of moody elements like storm clouds, dirty grunge, chimney smoke, etc. I've done some outer space themes and used Hickory Smoke instead black for outer space because other elements are easier to stamp or collage on top of it.
What else I love most about this grey is it being fairly neutral, neither hot (red shift) or cool (blue shift). Being neutral means that it can work stamped onto colored papers and not looks funky (like stamping on yellow and having the ink looked greenish).
I actually recommend that beginners pick up this stamp pad. It is so versatile and produces great results with little trouble. I have plenty of grey stamp pads and dislike 90% of them, but Hickory Smoke is by far the best.