Well... All the adjustments done in the RAW File are stored in 2 ways: 1. encrypted into the Lightroom Library like it does Aperture with its Library. 2. Written in an XMP file, which is just a file that can be opened with TextEdit. Each adjustment you apply to the RAW File is automatically written into the XMP file. There is an XMP file for each picture.
This is how it does look an XMP for inside:
<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Adobe XMP Core 4.2-c020 1.124078, Tue Sep 11 2007 23:21:40 ">
And it's quite longer. However, the file size is 3 KB.
Okay, if you change the location of the XMP (or delete it), the RAW adjustments are lost, so they should remain in the same folder where the pictures are stored. Each time you create a new Library in Adobe Lightroom and import pictures to that new Library, LR reads the XMP information for each picture and applies that info to the proper images and accordingly, and that way, you never lose your adjustments (unless you lose the XMP File). This is why is much easier in Lightroom importing adjustments from a Library to another if needed a heavy clean up. You can delete your catalog of pictures entirely, then import it again, to a new Library for example, and LR will apply the same adjustments to the "new" pictures by using the XMP files.
In order to activate this XMP feature, you should go to Catalog Preferences (or Settings), chose the Metadata Tab and check "Write changes automatically to XMP". From there, LR will automatically write XMP files for all your pictures, from the imported to the ones you're going to import.