I am as you know currently working with the Transposition Table. It is some hard work to get it all working especially since I am going to rewrite the way I handle the principle variation as well.
I am taking it a bit slow since bugs in the hash tables are nasty and can pop up when you least expect it. One game the engine is playing perfectly and the next it looses a queen for nothing.
The supercomputer Hydra did such a mistake in a tournament a year or so back. Sacrificing a piece for nothing and its evaluation did not drop until the next move when it realized its mistake. That was due to a hash table bug.
I am also configuring Eclipse to get it to work as I want (black text on white background hurts your eyes after 10 hours :). The first experiences with it has been rather nice and I will probably keep it. Though it does take some time to get used to.