A lot of good points made here.
I agree with Zev and others... Moving between the tree, Playing Now, and the Playlists is much too difficult. I think a navigation tool like "My Sidebar" on Netscape 7.0 beta would work well here. Tabs for Media Library, Playing Now, and Playlists would always stay on the screen. When you switch to Playing Now, the Media View tree can stay on the screen. You also wouldn't need a toolbar button to switch to Playing Now because the tab will always be there. You'd also reduce the need for the "Previous" button.
The [Shift]|PLS|[Delete] short-cut is a good example of how MJ is so difficult to use. You've got great features, but they're all hidden away.
And I agree with George... You've directed all technical support to this message board - a wise business strategy - but the board is dominated by a close-knit user community. And if no one is in the mood to answer a question at the time, then the user is out of luck. That's fine for freeware, but not for purchased software.
Did I mention that I love MJ?