I can easily get 400 connections with a simple setup and some minor code changes.  How many people would need to have the same setup and then pool the data to have 90% confidence that they know the ip address of the initial transaction?  Is that even possible?

Suppose there were 'n' computers with this setup, each with ~400 connections that log the time they first see a transaction.  The one 'n' computer that saw the transaction first would most likely know the originating ip.

Alternatively, Could/Would you have to map out the network (i.e. know who is connected to whom) to figure it out?

I agree that once a client has 8 connections it won't connect again, but I believe that disconnections are fairly common.  Just check the 'debug.log' file in your bitcoin client data directory and look for 'disconnecting node'.

--E