Legal question regarding rippling balances between Ripple gateways Let's say a ripple user were to extend trust to both Bitstamp and Snapswap to owe him 100 USD. He offers to trade USD-Bitstamp-IOU for USD-Snapswap-IOU at an exchange rate of 1:1.

Would he have to register this activity with a USGov institution? Would taxes on this transactions be due?

What if he did the same with an exchange rate of 1:1.01 and vice versa, i.e. taking an exchange commission of 1%?
In the U.S., FinCEN has specific rules regarding money transmitter laws for those providing money services.  Users who simply patronize a money service are almost never considered money transmitters or providers of a money service.  So, in your example, the answer is likely to be no -- no, a withdrawal from one service and a deposit to another would not likely cause you to need to report the transaction to the government. 

As far as taxes, that too is jurisdiction-specific.  In the U.S., capital gains taxes may apply however in your example there was no gain so there would then likely be no need to report the transaction on the tax forms.

Disclosure: I am not a tax advisor.