Cool thing #3: Using rvw! and del.icio.us to show a list of your reviewed albums in each year (for example, here are some of my favourites from 2004). I just added date tagging, so any previously posted reviews won't contain it.
You don't seem to be able to do the same thing including everyone's reviews yet. Also, as del.icio.us is not a proper reviews database, and so doesn't have special fields for each kind of metadata, you're not able to sort by rating or year. Still, it's a good start.