Your metadata is stored, primarily, in the MySQL database on your core. If you reinstall, you can tell the install to retain this.
Moreover - all metadata for mp3 files is stored in id3 embedded tags within the mp3 file itself, and this meta data is read into the database from these tags when a new system is built... so you do nothing to achieve this. Metadata for all other media is stored in an id3 tag file, alongside the actual media file, with the same name (ie, mediafile.avi and mediafile.avi.id3), as long as you keep those files in the same locations, a new LMCE installation will read the metadata back in from them.
Only things like Playlists, etc are lost. But there is an import/export function for that now.