After no significant attention to this area for years, there is a much greater focus recently on filesystem technologies. 

Over at Slashdot, Hans Reiser of the ReiserFS project is being interviewed on his open source filesystem project. There are some interesting concepts here, particularly the aggregation of small objects at the filesystem level and the use of balanced tree algorithms as the foundation for the filesystem. If you're interested in the innovations and advances in filesystem technologies that are going on right now, take a look.