There are some Windows software packages out there (ie Eclipse, VLC prior to its current version) that do not rely on an installation wizard. Instead of using a wizard there is simply a folder with all of the necessary components, from which you run the software. At no point is it actually considered "installed" by Windows. What is the impact on the user's experience? Many have become accustomed to installing software through a wizard, does this confuse people? Granted the two products mentioned are geared towards more technical people, is there any research that sheds light on the installation process?
UPDATE: Mac OS X often uses a process that involves dragging a folder to the Applications folder, but OS X recognizes these applications as "installed". This is Apple's simplified version of an installer (although it does often require a few screens of options). This process is expected by mac users. However, Windows users are accustomed to a multi-step wizard.