Will installing the Voodoo lagfix clear all my settings? I want to install the Voodoo lagfix on my SGS with Froyo.  Will this wipe my settings, or can I install it without worrying about it?
No, it shouldn't have any effect on your settings or apps. The FAQ from the Project Voodoo site notes:


  Will I lose any settings or App?
  
  None. But some sort of backup is
  recommended of course.