We've been following the attacks against Estonian servers for almost a week now.
For a good summary on what's been happening so far, read this article from Helsingin Sanomat.
Since that article was written, there's been one arrest ("Dmitri") in Estonia.
Here's an example of a Russian hacker site, offering Denial-of-Service tools crafted for this particular attack:
In addition to DDoS attacks, there's been some defacement activity.
Here's an Estonian website, defaced by Russian hackers:
And here's a Russian website, defaced by Estonian hackers:
On many Russian-speaking forums, we've seen discussion about starting a massive attack today, on the 9th of May – as this is a Victory holiday in Russia. And sure enough, after three calm days, just after midnight we saw a large botnet attack against multiple Estonian targets.
We probably haven't seen the end of these attacks yet.