It goes without saying that a tx can't go in a block if it's predecessors are not in blocks. I wonder if a single faucet txn getting dropped could lead to a whole chain of them being blocked?
Transactions seem to be being processed 'up' the chain (the opposite direction of the arrows), albeit very slowly. Usually only 1 in a block, but
http://blockexplorer.com/b/111261 contained about 10 in a row (from the same chain).
ps. the green was my attempt to highlight transactions that have been confirmed, but my data for that was unreliable/wrong.