AFAIK, openSUSE KDE Team backports important features and bugfixes to current released distribution.
Where can I learn about it and see the list of backported features?
There is a KDE Backports repository which you can add with YaST. Simply search that for a package you want.
You will also find back ported packages in the Build Service.
You didn’t understand. I mean backporting patches, not packages. For example, in KDE 4.3.4 release plasma pixmap caching bug has been fixed. If the patch will be ported to KDE 4.3.1, where I can find information on it?
I think the answer is that it won’t; the assumption is that you will upgrade to the newer version. Bear in mind that a lot of the work on KDE is done by volunteers who would rather spend their time improving the latest version than patching earlier versions.
The only patches you will normally get to earlier versions are security patches.