I hear more and more that photographers who use Lightroom are now using Elements as well (as opposed to Element’s big brother, the full version of Photoshop). Honestly, I can’t blame ‘em. Elements is a hugely powerful program and I think for a lot of photographers out there, that just want basic cloning/healing/layers/selections/retouching, it’ll take care of most of your needs.
There is a trick, however, if you’re setting up Elements as an external editor with Lightroom (on the Mac that is). First, you go to menu to Lightroom > Preferences and click on the External Editing tab. Now, your first inclination (at least it was mine) is that you go to the Photoshop Elements folder and select the first Elements application icon that you see for your editor. But if you do, when you try to edit a photo in Elements you’ll see the Elements interface open, but the photo will never show up. Here’s the fix. Instead of choosing the Elements icon in the main application folder, you need to go to Applications > Adobe Photoshop 11 > Support Files and choose the Adobe Photoshop Elements Editor.app file. Here’s a screenshot of what it looks like.

Now when you go to edit your photo from Lightroom in to Elements, it’ll automatically create a copy and launch Elements for you, and the photo will automatically open. When you’re done just choose File > Save and return to Lightroom to see the edited version.
From what I’ve heard, this has always been a big stumbling block for many Elements users so I hope this helps out. Take care!