Plugin
 

There is a very useful plugin I have seen once that works like this: You select a polygon and the plugin "switch it" to activated points - convert selected polys to selected points. But the problem is that I have forgotten which plugin this is. Can somebody help?

Don't need a plug-in. Go to the select tool near the top and use Select Switch from the list.

:beer:

Thanks TowerFan, there it is! I had used it once, but forgotten what the command was called.