It was 2 years ago when we started working in KDE 4 packages, and exactly 20 months ago when we started uploading KDE 4.0.0 beta 1 to experimental. Finally, we are working in packages that are targeted to unstable \o/.
As announced in the users mailing list, we will be uploading KDE 4.2.2 to unstable in the next days, so look carefully at what you update :)
We have worked very hard in providing a smooth upgrade, but given the change is so big, some new (little!) problems will be discovered. One of the most problematic points is we were using .kde4 to store user data and settings of KDE 4 and now it is time to switch back to the default .kde. There are several possible migration cases here and for allow users select the case they prefer, a migration wizard tool named Kaboom has been created inside the Debian KDE team.
Be aware that there will be some inconsistencies in unstable the following days after KDE 4.2.2 reaches the archive. So please, be patient.
We are still testing and we are not uploading until we think it is good to go, so next days could become 2 weeks. Again, be patient :)
If you want to keep using KDE 3.5.10 for a few weeks more, just do not upgrade yet. But if you want to keep using KDE 3.5.10 for months, maybe you should consider become a Lenny user.
Time for a personal note. KDE 4.2 is a huge change from KDE 3.5, and it is normal if you do not fully like it in the beginning. But I do think most of users of KDE 3 will feel very comfortable in KDE 4 after some days using it. You just need to discover the new ways of doing some tasks. Also, once KDE 4.2 is sitting in unstable, a lot of third party applications (specially plasma widgets) for KDE 4 will be finally uploaded to the Debian archive, making KDE 4 even better.