Lightroom now offers dual monitor support and clicking on the screen icons at the bottom left of the first column brings up a second window that can be placed on the second monitor, if you're lucky/rich enough to have such a set up.
Once you have chosen or found your image or multiple images you can then open then in the Develop module as before, or you can open them in Photoshop or another external application. You can do this at any stage of the process.
Unlike Lightroom v1, the export dialogue doesn't give you an option to open as a PSD or TIFF file or set the bit rate of 8 or 16 bits. I was annoyed about this at first, but never fear, the options are now in the Preference panel. In fact this is better, as most people have a set pattern of workflow - I always use 16-bit PSD, so once set in the preferences I can now forget about it. Furthermore, instead of generating a PSD file in Lightroom then opening in Photoshop, which is time consuming if you open multiple images, the files open in Photoshop and are saved back into Lightroom as PSD copies once they are closed in Photoshop. This speeds up workflow considerably.
Further integration with Photoshop includes the option to open the files as Smart Objects, with support for High Dynamic Range and panoramic stitching from multiple files directly from the ‘edit-in' dialogue box, again speeding up the workflow for fans of those processes.