I use quite a bit of material from "across the board", as it were.
However, I wouldn't shoe-horn in anything that didn't fit. For instance, quite a bit of the Eldritch books I like, but running a low-magic setting, not everything's going to fit if I just "drop it in". I plan to use most of the material, but it will be spread out so as not to add a new level of magic immediately. Certain Feats become "forgotten lore", and can only be learned about in the most ancient of tomes, while others are guarded knowledge, and the secrets of them are in the possession of but a few. All have been reviewed for ease to obtain and, when it seemed proper for the campaign, tweeked or re-prereq'd for setting-balance. The spells, rather than granted freely, are distributed to specific Prestige Classes, adding as much flavor as power.
On the opposite end of this is The Sovereign Stone. Great concept, fairly well written, but unfortunately not much about it will "fit" the game I'm running, and aside from the Bestiary, little in the setting has inspired anything for my game. Glad to own it, but it will likely collect dust until I decide to run a game with more in common with it.
The middle ground is where most books fall in. A fair example of this is Elementalism by Mongoose. It works as a concept, but much of it assumes a magic-rich world. Thus, many of the concepts are easily enough used, but instead of being "purchasable" via Experience Points and money, it becomes the ability of a Prestige Class designed specifically for it.
Along side that is Epic; While there are few things in it that I have rejected by reason of flavor, nearly half the book lies behind a line I've "drawn in the sand" refered to as "The True Name Mechanic", which designates a difference between "High Level" and "Epic Status" games.
So, honestly, I don't really "try" to use material; It either fits or it doesn't, and it usually fits in a way that it wasn't originally written for. About the only thing I don't ever bother with would be Prestige Classes, which I ignore to the point of almost never reading them (although I have gleamed an ability or two from a rare few to use in different ways or for a different Prestige Class).