My rule is that as long as its WOTC, and someone can bring an actual bought-at-the-store copy of the book to the table, then its in play. My guys aren't power freaks and I know they're more into the flavor and style than the power ups...so I'm comfortable with it.
Also, most of em are too cheap to buy extra books.
As a DM, I tell the players "Hey, I got this book, check it out. Don't be surprised If some NPCs are using some of this stuff"
As a player, I'd just figure out what class/feat/whatever I want to use and take it to the DM. I wouldn't just hand him the book and say "can I use this book?"
I'd only get perturbed if he dismissed it out of hand just because it came from a splatbook. (Fortunately, you can spot these guys a mile away, usually well ahead of time. So you can spare yourself the hassle.)
But then again, I'm always the DM in our group, so it doesn't matter.