Final version of KDE 4.1 has been released officially today. It was on schedule release (great job to KDE team), but don't think that 4.1 will have all the functionality that you might expected as in 3.5. KDE 3.5.x is a very mature release and it would take some time to make all of the features in 3.5 to be implemented in 4.x.
The feature plan document lists all the features list along with the current status. Most of them are marked DONE, but some are still in progress and also in TODO list.
At least for now KDEPIM is back and people who used KMail or Kontact can use it again as they have been restored in 4.1. For application that didn't make it into KDE 4.1 will have to look on this Schedule Plan. It includes big pile of major application, like Amarok, KOffice, K3B, Kaffeine, and KDevelop.
Still not convinced with KDE 4.1? You can wait for the next update in October (KDE 4.1.1) or KDE 4.2 in January 2008. If you are still using KDE 3.5.x and feel that it's the right version for you, then don't worry that it will abandoned. KDE team is planning to release an update to KDE 3.5.x, which will be KDE 3.5.10 and it is scheduled for August (that should be in a few days, but we don't know the exact date yet).