yes, I've upgraded our website to OJS 2.4 and the inline PDF-display is ok for me. Here's an example abstract with links to the PDF:http://www.reinhardt-journals.de/index.php/peu/article/view/3841
However, when dealing with the display of PDF files in browsers you should be aware that some browsers and/or Adobe's PDF software have some user settings that define if PDFs are to be displayed in the browser or in external program windows. Firstly, your browser needs to have a PDF plugin. And secondly, you should have set PDFs to be displayed in the browser.
Note also that OJS has some fall-back behavior: In case a PDF plugin is not installed for a certain browser, it would display a message telling the user how to install the plugin. This works for me, too.
What exactly are your problems with the PDF display?