Quoting Neil Hodgson from PySide mailing list[1]:

Both PySide and Shiboken publish .pc files so that pkg-config can be used to
find build parameters. For example, to link to PySide it should be possible to
find the correct libs with

pkg-config --libs pyside

   On my Linux machines this produces

/usr/lib/libpython2.6.so -L/usr/local/lib -lpyside -lshiboken

   However, the files in /usr/local/lib include Python version tags in
their names

libpyside-python2.6.so
libpyside-python2.6.so.1.0
libpyside-python2.6.so.1.0.4

   This makes it more difficult to produce generic build files. Since
qmake supports pkg-config, it should be possible to include these
commands in a qmake project but this does not work:

CONFIG += link_pkgconfig
PKGCONFIG += shiboken pyside

   The relevant pkg-config file pyside,pc looks like this:

------------------------------------------------------------------------------
prefix=/usr/local
exec_prefix=/usr/local
libdir=/usr/local/lib
includedir=/usr/local/include/PySide
typesystemdir=/usr/local/share/PySide/typesystems
pythonpath=/usr/local/lib/python2.6/dist-packages

Name: PySide
Description: Support library for Python bindings of Qt-based libraries.
Version: 1.0.4
Libs: -L${libdir} -lpyside
Cflags: -I${includedir}
Requires: shiboken
------------------------------------------------------------------------------

   A solution may be to include the python version tag in the relevant
variables like

Libs: -L${libdir} -lpyside-python2.6

   The pyside.pc file has already been specialized to Python 2.6 by
the pythonpath variable so it is not losing any generality.

   I have seen this issue with packages downloaded using apt-get on
Ubuntu and yum on Fedora as well as when built from source.

[1] http://lists.pyside.org/pipermail/pyside/2011-July/002696.html