I talked at a hacker group here in Mountain View last night.  They were very interesting.  They have a few questions that I couldn't answer:

* Who gets the txn fees that are put on small txns?  I sent a small txn to another wallet of my own, and was charged a small fee.  Who got that fee?  I did not get it, and nobody else took part in the txn!  Where did that money go?  Who got that money?

* How is balance within a coin tracked? - The transaction list is a clear concept as I presented it, but I present it as if the bitcoin were an atom which is not true.  How is subdivision of a bitcoin handled?  The balance and the ownership of each fraction will need to be tracked and checked for each txn and if there are many small ones they would be scattered all along the block chain which would make validating a single txn inefficient.

* selfish blocks - A node could pretend to receive no other txns except its own txn 0, and simply focus on hashing.  This would be an unfair an advantage, though a small one. Sounds feasible but not scary.

* Takeover the irc server and direct all new peers to a darknet of their own controlled nodes so they can establish their own dominant block chain. 

About the talk: It was a South Bay hacker group called DC650 at the Hacker Dojo.  I was referred to them by the folks from the SF hacker group where I spoke on Sunday.  I did a speech for over an hour, and then we did questions for another hour.  It all went very well.