There have been many questions about the 4.x releases. I'll try to shed some light on this:
The 3.9 branch has finally reached it's end. The last one of the 4.0 preview releases will be 22.214.171.124. It will be updated with the new logo (as soon as it's finished) and then released as 4.0
4.1 versions are going to include many new features. An alpha version will be made available for paid users as soon as the first new functions are finished.
While 4.1 development has been started in 2007 there have been many delays. We hope to get the first alpha out before the end of Q2/2008, but no promises can be made at this time. ;-)