More in the annoyance category, and not rating a separate thread, anyone interested in the new Mac Tiger OS may want to take a quick look at Malicious Widgets May Torment Tiger Users eWeek, By Robyn Weisman, May 9, 2005.
The Tiger OS isn't too widespread yet, and appears to be really good. Patches should be availabe for "widget management" by the time most people will need to be concerned.