The layered navigation (since Prestashop 1.4 but, really usable in 1.4.5),  allows users to define in a simple way some criterias to filter category products (as you can find on CalumetPhoto or other shops).To use it, it is very easy : just define « templates » (group of criterias, like features (capacity, etc), brands, stock level).Once it have been done, you will be able to to link these templates to categories, for example the « DSLR cameras » for the cameras categories.
Each template can be used on as many categories as you want.

To use layered navigation, just follow these steps:

• In back-office, go to Modules / Layered navigation block
  
• Go to Build your own filters template and check Specific categories (0 selected):
  
• In the block which appears, please select the categories on which you want to apply this template and click on Save this selection:
  
• In the criteria list, you will be able to select some of them, by checking it:
  
• Let’s give a name to this selection and click on Save this filter template

With the example data above, the resulting block on the front-office will be, only for « Accessories » category, something like that:

Beware : the available criteria depend on the category you choose.

In our example, the products have not « features » (in a Prestashop way). But if I select the « iPods » category (iPods have « features »), the choices I can made will be different: