OK.
I managed to install qwtpolar and add a plugin to qtcreator. Complete steps, that worked for my Ubuntu 12.04:
1) first of all we need to have installed qt4 or higher dev libs, qtcreator, qwt dev libs.
2) download sources from svn (not archive file but svn!) and follow steps in README (qmake & make & make install)
3) to add a qwtplugin to qtdesigner you need to do the following (replace x.x.x with qwtpolar version):
sudo ln -s /usr/local/qwtpolar-x.x.x/features/qwtpolar.prf /usr/share/qt4/mkspecs/features/
sudo ln -s /usr/local/qwtpolar-x.x.x/features/qwtpolarconfig.pri /usr/share/qt4/mkspecs/features/
sudo ln -s /usr/local/qwtpolar-x.x.x/lib/libqwtpolar.so /usr/lib/
sudo ln -s /usr/local/qwtpolar-x.x.x/lib/libqwtpolar.so.1 /usr/lib/
sudo ln -s /usr/local/qwtpolar-x.x.x/lib/libqwtpolar.so.1.0 /usr/lib/
sudo ln -s /usr/local/qwtpolar-x.x.x/lib/libqwtpolar.so.1.0.0 /usr/lib/
sudo cp /usr/local/qwtpolar-x.x.x/plugins/designer/libqwt_polar_designer_plugin.so /usr/lib/x86_64-linux-gnu/qt4/plugins/designer/
4) run qtdesigner and voila! There is a new QwtPolarPlot tab.
5) to run a qt application with qtpolarplot you only need to add 2 lines to your *.pro file:
INCLUDEPATH += /usr/local/qwtpolar-1.0.0-svn/include
unix|win32: LIBS += -lqwtpolar