There is no way that I know of that this plugin could cause this to happen. Could you be more specific?
1. What do you mean by ‘wiped out’ your installation or ‘destroyed all control over themes’?
2. How do you know this plugin specifically caused the problem?
3. Have you checked apache/php error logs to see what actual bit of code is causing trouble.
Let me know, if this plugin is somehow breaking thing I’d like to fix it.
Edit: It would also be useful to know what version of WordPress you are running.
Edit #2: Just thought of this – what hook did you try to place here? If you put something like init in the widget, or something else that already has a whole lot of core-related actions attached to it, that could and probably would cause some kind of crazy error – but thats not the widget causing it, thats due to the hook you chose to use.
If this is the case, best I can do is place a warning in the docs explaining to use with core WordPress hooks at their own risk. Like hooks in general, this plugin does give you enough rope to hang yourself with – all this plugin is, is a hook wrapped in a widget.