One of my favorite features that was recently added to the RCSB PDB site is the drilldown of search results. In this release an extension to this was added. It is now possible to drill down through EC numbers as well as through the SCOP classification.
A useful trick, that some people might not have noticed yet is that the drilldown is available for the whole set of PDB entries. By clicking on the total number of entries on top of the page one can access this faceted browsing interface over the whole database. The screenshot below shows where you have to click to access this feature.
After clicking on the total number of entries here is the drilldown for the whole of PDB: