Why in the repositories (and the wiki) KDE 4.1 is called “factory”, while KDE 4.0 is called KDE 4 Stable? Obviously, KDE.org states otherwise, that 4.1 is the stable release, while 4.0 was an older and less stable release.
I have to say that KDE 4.1 is really more stable and should be recommended. Haven’t seen a single crash report, while when I had KDE 4.0, there were loads of them. 4.1 is actually so great, that I have no idea why so many people still use KDE 3.5 
The integration of 4.0 into openSUSE is complete and the result is a wobbly one. But it’s finished for what it’s worth.
The integration of 4.1 into openSUSE is incomplete – hence “factory”
if i’m not mistaken it is because it is actively being developed and there could be problems with the updates which have happened
but i use 4.1 also and it is really stable and have no problems with it
stable is the current version that is supported by opensuse
factory is the current version that is being worked on for the next release, but is not supported in the current opensuse release
unstable which is 4.2 is not supported in the current release, and isn’t getting that much work on so lacks the opensuse feel to it, but is actually coming along very good, and is whatI use