@benZin: Just enable 'Always write ISO-8859-1 tags instead of UTF-16' at 'Options > Tags > Mpeg'. Seems that your portable doesn't support ID3v2 tags written in Unicode.
freedb is working fine as long as a working freedb server is selected at 'Options > freedb > Server'.
As freedb.org has problems with their main rotation server freedb.freedb.org at the moment, I suggest to switch to one of the regional mirrors...
Read full review
Mp3tag has support for AMG, artistdirect.com, discogs.com and musicbrainz.org via the Web Source Framework and it's easy to build a custom web source for amazon.com. Just suggest this on the forums and someone will do that.