I can post a screenie tomorrow if anyone is interested.
Actually, that would be good if you could.
Personally, at this stage I couldn't live without the tree ~ I have too many things packed in there for it to be effective as a tab system. I have separate levels and sublevels for organisation of albums, films, television, books, photos, comics, music videos, coverart, games and some limited document support... the list goes on. The only issue is that my tree has become very large and often requires too many levels to get to where I want.
One thing I would like to see with tabs though would be the ability to switch between media modes (kind of like the current imlementation of "All Media", "Audio", "Video" etc" but with customisability. I would like to be able to make my own modes (eg. "Books") each with its own filters and own unique tree.
The current problem I have (with the way media modes split the library by Media Type: video, audio, image, document etc) is that some forms of media overlap between these categories. For example, my "Sheet Music" collection contains a mix of image files, pdfs and finale documents, so some of them appear in "Images" and some are in "Documents".
As MC has always been promoted as "The one that plays them all" (and it does this better than any other program I've come across) there is definitely room for more comprehensive organisation of large & diverse media collections...
Maybe tabs are the answer, but they should be used to supplement the tree/view schemes, certainly not to replace it.