I have my music collection in folders by artist, then album.  The problem I'm running into is that for some albums, I have them in a lossless format (.flac) and mp3.  I keep the MP3's around to easily transfer to a portable player and use the lossless for listenning to in and around the home.  When using Amarok's Collection view, I would of course get one album listed with twice the songs (both the mp3's and the flac's).  So to distinguish between the two, I retagged the album field of my lossless albums such that the album name is appended with '- lossless'.  ie.  I'd have two albums: 'Meet the Beatles - lossless' and 'Meet the Beatles'.  This method cleaned up my Collection view in Amarok.  The only problem I now have is that when I use the Context->Current view in Amarok, it doesn't pull in the current album information as it's looking for an album named with the text, '- lossless', attached to it.  Is there a better way for me to handle duplicate albums in a way that my Collection view is still seperate?  If not, I'd like to request this feature.

I forgot to mention, now that I've retagged my lossless albums, I find it useful to put the text 'lossless' into the search on the collection tab and I can get a nice listing of all my lossless.  This is quite handy for reference listening.  I'd like to be able to keep this feature, as well as keeping my duplicate albums separate in the collection tab and be able to use the context tab.  Anyone have any thoughts?

It is sortof a non-answer to your question, but one option would be just to keep the lossless, and transcode on the fly
using the transKode plugin.  It depends on how fast your computer is, but for me, transcoding an album from flac to m4a is not too
bad.

I think the question of duplicate albums might be interesting anyway in the context of having e.g. a collection on a laptop, and
a larger collection mounted from a server.  No idea what to do about that, unless there is magic in the "dynamic collection" support
in the latest amarok's

I'm on the same situation, except I don't want to re-tag my lossless files with -lossless.
It would be good if I could at least filter the collection viewer by filetype. or be able to search by filename

the anoying thing is that it displays the album with duplicate tracks and there is no way to add only one filetype to the playlist.

You could keep your MP3 and FLAC files in different folders.  Then just tell amarok to add the FLAC folders to the collection.