Three aspects of this investigation stand out to me: The crowd sourcing aspect, the amount of openness from the Government (I found myself going to the Boston Police and FBI websites for news as much as any of the media outlets) and the Government / private citizen cooperation.
Over time, with a lot of detailed analysis of the unfolding events, I'm sure plenty of people will find plenty of things to question, but when something unfolds that fast, it's amazing that anyone can keep anything straight.
Two separate trends came together for forensic success in this case: the existence of fixed security cameras and the near ubiquitous presence of media / personal cameras at a popular event. Crowdsourcing in criminal investigations is an emerging trend (and one with a dark side when false accusations are made early in the process).
"... much to the chagrin of privacy advocates."
Would these privacy advocates have preferred that the Tsarnaev brothers had gotten away to perform their deeds elsewhere? They were apparently bound for NYC. The presence of cameras made their identity known in record time.
One problem I see is that many of these same privacy advocates also oppose strict immigration checks, which may have helped in this one case, at least. The FBI had been warned. Of course, immmigration checks would have done nothing in many other recent high profile cases, but cameras can and have helped every time.