This post is long overdue. I downloaded this back in February, and promised a review, and well, better late than never, I suppose. Over at Hack & Slash some months ago, -C compiled a great free downloadable netbook called "Tricks, Empty Rooms, and Basic Trap Design." The book is simply 30 pages of nothing but awesome. Whether you're a novice DM or an old experienced dungeon builder, you'll find plenty of useful information in this free supplement. I'd say that along with the Dungeon Alphabet, this may be the most useful resource I've found on dungeon design within the OSR community.
Essentially the book covers the elements of basic trap design, along with examples of said traps, descriptions and tables to liven up those empty rooms in your dungeon, various tables to help you design some wonderful tricks, and a great section on magical pools and fountains. The random tables included allow you to essentially build a limitless amount of traps and tricks to populate your dungeon. Yes, there are other supplements out there which deal with these elements, but none that I've found that manage to do so in such a succinct and detailed manner. This, in my opinion, is one of the must have books of the OSR community, especially considering he's giving it away!
I have been using this book as a great reference in my own megadungeon project, Dreadrock Dungeon (the first section of which is available to download now), and I plan on giving him an official acknowledgment when I compile the entire megadungeon project together. So, if you haven't already, and I suspect that many of you probably already have, get on over there and download this awesome supplement. And thank you -C for this wonderful contribution to the OSR.