Facts of 1st attack: a Georgian account in Twitter, Facebook and Google’ blogger, was targeted by multiple attacks. It caused Twitter to shut down, Facebook had problems. And the suspicion is on Russia, obviously (although it remained to be proved).
Apart from the costs of it all, what is interesting is the fact that the attack against one person/entity triggered problems for everybody else using the services of Twitter, Facebook and Google. The collateral effects are damning.
Blogger targeted in Twitter, Facebook DoS (ZDnet.co.uk, 7 August 2009) and Cyberattack That Brought Down Twitter & Facebook Only Highlighted The Guy It Hoped To Silence (TechDirt, 10 August 2009)
French version: Twitter rendu indisponible par une attaque visant un internaute (JDN, 7 August 2009)
Facts of 2nd attacks:
Twitter suffers outage following fresh attack (ZDnet.co.uk, 12 August 2009)
To which extend the botnet was part of the 2 attacks, it remains to be seen: Security firms reveal botnet on Twitter (ZDnet. co.uk, 17 August 2009)