Some time ago I wrote that I am considering switching back to KDE 3.5 after few months with KDE 4.0/4.1-svn. Finally I did it.
Reasons are the same as in previous post — lack of stability and I for now I do not see bright future for KDE 4.1 (but this can change after release if developers will work on fixing bugs instead of adding new features/rewrites). With 4.1 svn snapshots there was guessing ‘what is broken today and how badly’ — mostly Plasma desktop was more or less unusable. For example panel which works in 4.0.72 stopped working with 4.0.73 unless enlarged to normal size, second panel nearly never worked (or even made Plasma crash each time).
So for now I am back on KDE 3.5 with few components from 4.1-svn (window manager, Okular, Dolphin) and wait for 4.1/4.2 releases to have something to test.