I spent the last few hours trying out Lightroom and decided I quite liked it! And then I realized that it does not create the sidecar files for the RAW files the way that ACR does (or even the way that Silkypix does, in a separate subfolder).
I usually archive my RAW processed files by backing up the RAW file to DVD, including the sidecar files. Where are the sidecar files for Lightroom-edited RAW files? Is there an easy way to archive the "processing" that goes with the RAW files?
You can automatically 'Write XMP to File', but it is tedious and slows it down. It also writes INTO Jpeg, Tiff, PSD and DNG.
I would recommend selecting the files you want to export in Grid and then go to menu :Metadata>XMP>Export XMP to File
Then backup those folders.
You could also, if you like use Export and create an Export Preset to 'Burn DNG to disc' and have the metadata embedded this way.