Well , security wise if you made it that far and all across Brazil you shouldnt have problems, just dont leave your bike unnatended becuase it will be robbed, same thing for any luggage. Bs As, is a nice city, in economic terms you can use CC or USD, cash usually gets you better deals, but be prepared to spend as much moeny here as you'd do in USA. Argentina certainly isnt cheap, not any more.
I'm planning a motorcycle ride from the U.S. to Rio over December 2010 through February 2011. I keep hearing about Buenos Aires and how wonderful it is. I know there were some serious problems there in the not-too-distant past. What is it like now?
I may want to come back after Rio and spend some more time there - what is your economy like, generally?