This is a new feature added to the latest version of UnrealEd.

Basically and brush created belongs to a group called "None".

If you select a number of brushes and click the New Group icon then they are automatically added to this new group. However they still belong to the "None" group but can now be removed from it...

Icons

	Dock/Undock browser
	Create new group (you must have at least one brush selected to do this!)
	Delete group (this does not delete the brushes)
	Add selected brushes to the selected group
	Delete the selected brushes from the selected group
	Refresh the group list (e.g. any groups no longer containing any brushes will disappear)
	select brushes in currently selected group
	de-select brushes in currently selected group

Brushes will only be shown in the 2d views (has no effect on 3d views) if all the groups they belong to are ticked. e.g. If they belong to Group1 and Group2 and you untick Group1 then they will disappear.

Note: Group information is saved with the map.