One of the best new features in Blender 2.5 is the concept of the 'operator tweaking' which means that the user can change tool settings after the tool as applied and see the results immediately. Basically the equivalent of 'what you see is what you get' (WYSIWYG) editing. With the toolbar open, the bottom bart of it contains these settings. This is nice, because it fits with the non-overlapping UI model.
The problem arises though when the toolbar is closed, because these settings are no longer accessible. This turns out to be a rather large issue, because many tools effectively become unusable, with no way to control them. For this reason I think adding a 'floating' panel makes sense. It should only appear when the toolbar is closed, and should not be blocking, ie it should not steal the users input.