to pthomas:
Here you can find a good explanation of changes in .ui files.

For coding you can still using KDevelop and manage .pro files by hand or by qmake if you rather prefer.
About subclassing ui, you can run uic by hand on the .ui file like:
Qt Code: 
  1. uic somefile.ui >somefile.h
To copy to clipboard, switch view to plain text mode 
and then use the header generated file as a normal file with a parent class definition.

Hope it helps.