Piggy Bank is an interesting little concept as it tries to bring together ideas about what the semantic web could be into a user-friendly Firefox plugin. There is also a server component for sharing your 'semantic banks' with others. The concept seems quite nice but I have really struggled with the user-interface. If anything the interface is too transparent and gives a view of the information that feels too raw for the casual user. For somebody that understands RDF schema some of the attributes are probably very useful but for the general user these things just confuse matters.
I do like the idea of communal bookmarking systems. Digg is probably the best example of a web-based bookmarking system and Piggy Bank just takes this idea one step further. To test things out I have setup my own semantic bank server at http://semanticbank.stress-free.co.nz/bank/. Registration for an account is done through the Piggy Bank interface in Firefox. The concept shows a lot of promise but needs a lot of tiding up and an interface overhaul before it will become really useful.