I am linking my plugin to qqmp qt-based multimedia player. Why cmake puts result in the projects top directory/libs? Her is a part of my makefile:
SET( LIBRARY_OUTPUT_DIRECTORY
${CMAKE_CURRENT_SOURCE_DIR}
)

SET( RUNTIME_OUTPUT_DIRECTORY
${CMAKE_CURRENT_SOURCE_DIR}
)

SET( ARCHIVE_OUTPUT_DIRECTORY
${CMAKE_CURRENT_SOURCE_DIR}
)


MESSAGE("LIBRARY OUTPUT DIRECTORY ${LIBRARY_OUTPUT_DIRECTORY}")
MESSAGE("ARCHIVE OUTPUT DIRECTORY ${ARCHIVE_OUTPUT_DIRECTORY}")
MESSAGE("RUNTIME OUTPUT DIRECTORY ${RUNTIME_OUTPUT_DIRECTORY}")

ADD_LIBRARY(qmmpkde4filedialog SHARED ${libqmmpkde4filedialog_SRCS} ${libqmmpkde4filedialog_MOC_SRCS} )
add_dependencies(qmmpkde4filedialog qmmpui)
target_link_libraries( qmmpkde4filedialog ${QT_LIBRARIES} -lqmmpui ${KDE4_KIO_LIBS} -lkio )
install(TARGETS qmmpkde4filedialog DESTINATION ${LIB_DIR}/qmmp/FileDialogs)

Well MESSAGE( ... prints my current source directory, and I wont the resulting lib to be placed there, but why it goes elsewhere? Thanks in advance.

All libraries are placed in BUILD_DIR/libs. This is so within project linking can be done easily by CMake. You should only be concerned with the location where libraries are installed.

While the reply likely was fully correct, it didn't quite tell the whole story:

Your LIBRARY_OUTPUT_DIRECTORY variable has the same _name_ as the _property_ to be set on a target (via set_property()). That, however, doesn't help much (in fact it's completely bogus since this variable isn't hooked up anywhere), since I guess what you really would have wanted is the builtin CMAKE_LIBRARY_OUTPUT_DIRECTORY variable for the _global_ setting, i.e. to affect output directory of _all_ targets.

IOW, _either_ set the LIBRARY_OUTPUT_DIRECTORY target property (_per-target_), such as:
set_property(TARGET ...
PROPERTY LIBRARY_OUTPUT_DIRECTORY ...
)
or some such, or:
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ....)