Just do it as aonsalthya explained. This is a simple and effective approach. Thx again

As a lot of others guessed, that it is DECW causing this, count me also to those:
I had to do a reflash and installed (almost) all of my programs, incl all widgets. I recovered my settings from a backup and detected an error in the .desktop_cmd_exec config file. I corrected this and had no freezes since then!

aonsalthyas solution is effective but I'd like the desktop to restart automatically because I believe that a frozen desktop resulted in me not receiving phone calls or sms messages.

I really hope to solve this without reflashing but good to know that it is an option. I guess I'll first have to learn how to create desktop widgets and try the idea dovf presented earlier.