I downloaded GRAVEL on day one and have been perusing it since. Like others on this thread, I'm rather impressed with it. As is usual for Mr. Stone, the booklet is well-produced, interesting to look at, and the illustrations are wonderful. The layout and details are first-rate.
And then there's the magic itself. With his previous .pdf releases, Tom revealed himself to be very clever (and perhaps a tad devious and twisted at the same time), and the material in GRAVEL is pretty solid. There are some full routines and some scattered ideas that can be plugged into your work (particularly the rope ideas).
He starts with The Test, a clever mental effect. It's obvious that Tom is a fan of Max Maven (aren't we all?), and this routine clearly shows that. The method is sure to baffle.
There follow ideas with chairs (a pretty good bit, I think), ropes (cut and restored handlings), and cigarettes (a very nice Slydini-like effect where a cigarette is broken in two pieces, and then each piece becomes a full cigarette in itself).
Another mental effect, Synonymax, which is a strong participation effect. Tom goes through the various ins and outs with good detail, and this is one that is sure to play well on stage.
There follow a couple more random ideas with coins and ropes before reaching a routine called Negative Spaces, the one that David mentioned in his post above. It's a very interesting spin from "Real Gone Aces" combined with the "Open Travellers" effect that launches in a direction of its own. Here, three aces are laid on the table while one is placed in the card box. Three indifferent cards are placed with the first tabled ace, and it simply disappears from within, leaving the three cards. Then the same three cards are placed with the second ace and all four are handed to a spectator. She counts them herself and there are only three -- no ace. Finally the same three cards are placed with the last ace, and it disappears as well. All are found in the cardbox. The approach is clever and clean, and I'm sure it will spawn variations galore.
Ever since reading my first Tom Stone booklet, I've been a fan. I'm happy to say that I'm still so, more than ever.