I like to view my collection browser with the tree view as such:
Label/Artist/Album
Upon closing and restarting Amarok (1.4.9.1), it forgets this, and I have to manually set it up every time I want to browse my collection.  Is there some way to have Amarok save this preference?  Thanks.

Odd that it's not saving the setting - you could try deleting/backing up the Amarok config file (~/.kde/share/config/amarokrc) and creating a clean one by restarting Amarok - sometimes this helps. If the probem persists, it's possible you've encountered a bug, in which case, reporting it at http://bugs.kde.org would be helpful!

Do other Amarok settings get forgotten too, or just this one?

It's definitely just that setting being forgotten.  I tried deleting the config file and letting Amarok generate a new one with no luck.  This is interesting:

[Collection Browser]
Category1=8192
Category2=2
Category3=1
Database AFT Version=2
Database Devices Version=1
Database Persistent Tables Version=19
Database Podcast Tables Version=2
Database Stats Version=12
Database Version=35
FlatColumnWidths=
ShowDivider=true
ViewMode=0


I assume that the group values are enumerated constants.  Artist/Album are numbers 2 and 3.  Why is label 8192?

EDIT:
It looks like the 8192 value is sane.  Code snippet:
namespace CollectionBrowserIds
{
    enum CatMenuId { IdAlbum = QueryBuilder::tabAlbum,
    IdArtist = QueryBuilder::tabArtist,
    IdComposer = QueryBuilder::tabComposer,
    IdGenre = QueryBuilder::tabGenre,
    IdYear = QueryBuilder::tabYear ,
    IdScan = 32, IdNone = 64,
    IdArtistAlbum = 128, IdGenreArtist = 256, IdGenreArtistAlbum = 512, IdVisYearAlbum = 1024, IdArtistVisYearAlbum = 2048,
    IdLabel = QueryBuilder::tabLabels //=8192
    };
}