Filters are a very powerful new tool available in Revit 9.
They give you the ability to control the visibility of any group of elements you define. Including their line colour, line style, and lineweight as well as whether that particular group of elements is visible.
They give the user the ability to control elements in way where previously mistreating worksets was the only method. Personally I still feel the need to control elements with worksets sometimes.
Before I begin with a quick tutorial, filters cannot be used on annotation elements such as section markers (unfortunately...)
Being by going to your visibility settings for the view you wish to add a filter.
Click on the filter tab.
Click Filters down the bottom.
Click New, to add a new filter.
Name it accordingly. Best to use something descriptive so you'll be able to use it again in another view at a later stage.
Select which element categories you'd like it to filter through... You can select multiple or single categories.
Select filter by... This enables you to filter from all the shared and project parameters available for these elements.
Then select the way you want to filter it (contains, equals etc)
Then type in the condition you require. (you can repeat this to set multiple conditions in a single filter)
Now insert this filter into the view.
Now all elements matching this criteria can be manipulated independently, either by turning them off, giving them a different line style (for example fire rated walls or structural walls...)
You can also access you filters through you settings menu.