You have got to be kidding me! I just bought elements 10 and and found out that when you use use lightroom you cannot simply save the file back into LR like you can in CS5. I want my money back, you mean you have to import the file back into LR? That is crazy, what a complete waste of time!
I think I can help you with this - I use PSE10 and LR3. Yes, you can save the file back into PSE10. But, if you already have CS5 installed, you may have to enable PSE10 as an additional external editor first. To do this, go to Preferences>External Editing. In your case, the top part of that dialog box is probably defined as CS5. If you want to continue being able to send images to CS5 at times, you'll probably want to leave that there. So, you'll establish a preset for PSE10. In the second section of the dialog box, called "Additional External Editor", click on the button that says "Choose" and navigate to the appropriate location and select PSE10. Then in the drop down just above that (called "Preset"), choose the option to "Save Current Settings as New Preset".
Once you've done that, you should be able to send the image from LR3 to PSE10 by using the Edit In command from the Photo menu or right-click and Edit In. If that does not open PSE10 for you, you may have directed LR to the wrong file when you set up the external editor. You must direct it to PSE10's Editor, rather than just PSE10. For Mac, the path to find that is:
Mac HD>Applications>Adobe>Photoshop Elements 10>Support Files>Photoshop Elements Editor.app
On Windows 7 (64-bit), the path is:
C:/Program Files x86.Adobe>Photoshop Elements 10> PhotoshopElementsEditor