Bootstrap 3.0 Button in Navbar

Wrap a <p class="navbar-btn"> around the <a class="btn">:

<nav class="navbar navbar-default navbar-fixed-top">
    <div class="container">
        <ul class="nav navbar-nav">
            <li>
                <p class="navbar-btn">
                    <a href="#" class="btn btn-default">I'm a link button!</a>
                </p>
            </li>
        </ul>
    </div>
</nav>

JSFiddle: http://jsfiddle.net/lachlan/398kj/

Screenshot: