[olympia]

1) I am pasting this http://www.allmusic.com/album/release/ba...0001055858 into an album.nfo inside the album folder. Then trigger a refresh but nothing happens, no new info populates the album. Same results with the Discogs' link to the particular release. Is it the allmusic link to the release inside the album.nfo what is needed according to this, isn't it? The only link that gives results, although imperfect, is the direct musicbrainz link to the release, however it brings back the general info for the release group with a review from wikipedia instead and neither from allmusic or discogs.

For the Universal Album Scraper you indeed need to link directly the MusicBrainz release page. The wiki page you linked is unfortunatelly wrong. Not sure who was creating it, I will get it fixed as soon as I find the time for it. Allmusic and Discogs link will not work. Discogs is not supported by the scraper at all, while it fills some database fields from allmusic, but only if the allmusic link is available on MusicBrainz. The ONLY supported site for 'Album Review' is theaudiodb.com (what you can edit yourself as well), so you are not getting the review from wikipedia. Once again, Album Review is not available from allmusic or last.fm or from anywhere else, only from theuadiodb.com. Not sure what you mean on imperfect thought...

2) I have 4 different releases (versions) of the album 'Bad' from Michael Jackson. When added to the library they are gathered together under one album and all tracks are mixed up. The metadata has been correctly saved differentiating each one of them by musicbrainz release year and contents, with Picard. Is there a way to avoid this, different than editing the album titles to a slightly modified name appending forms such as 're-release', 'special edition', etc...

I believe if you link the different releases from MusicBrainz via album.nfo that it should be OK, I never tested this though.

3) Is there a way in XBMC to define a set of albums (not the filter solution), e.g., the set 'Bad', and when clicking on it, then all the releases I have for the album 'Bad' including the original will show up as individual albums for me to select? Like sets in movie collections? So I can define my own sets of music albums?

No, this is not currently possible.