mwiktowy, I'm having the exact same prob, and it's driving me nuts. As seems the case for you, the workaround at the moment is to reboot or kill maemo-launcher.

I haven't done much troubleshooting yet. When I get a moment, I may compile the GNU version of ps and pstree to see if I can find an offending program. I seem to recall that top will display CPU usage for the parent application, so perhaps it is a sub-process that is causing the problem.

I'm also snapshotting running processes (ps > running_procs.txt) to compare what's running when this behavior persists and when it doesn't.

I'm wondering if an offending application may be leaving a process running after exiting, something such as WIFI connection or media player.