I think that Marin's two-volume opening repertoire based on 1.e4 e5 (Beating the Open Games and A Spanish Repertoire for Black) is amazing, and packed full of chess knowledge. However, the two books are targeted towards either more-advanced players (particularly the latter), or the ambitious student. They're also directed towards main-line players rather than offbeat-variation players. This means that the reader has to plug a lot of holes themselves, as they find that the opponents they encounter at their level frequently play a line not covered.
I just checked qualitychessbooks.com, and found that a 25-page addendum to ASRFB is available for download in .pdf format. It covers, among other gaps, my biggest problem with that book: no discussion of the departure from the Chigorin mainline with 12.d5 (instead of 12.Nbd2). I see the former more than the latter in my online games, and it's the #2 line by statistics (74 out of 1051 Grandmaster games, according to my home-made opening book; 478 out of 6050 games total).
In other news, it appears that the first volume (BTOG) is about to be reissued as a second edition. When I bought it, it contained a 4-page insert covering two omitted lines. It sounds like a combination of popular demand and reader critique has prompted an upgrade. According to the publisher, it should be out very soon (Spring 2008).
It's annoying when you just buy a book and a new edition comes out shortly after. When the second edition of Dvoretsky's Endgame Manual came out, I decided that I didn't need to worry about the second edition until I completed the first (which is still a loooooong way off). Also, I've heard the quality of print for the second edition of Dvoretsky wasn't as good. However, Marin's BTOG has become indispensable for me, so I'm looking forward to seeing what's been added in the second edition.
Real chess players will roll their eyes because I've held Dvoretsky on the back burner while salivating over an upgrade to an opening book. Well, like the banner says: Do as I Say, Not as I Do.